THE JOYFUL REDUCTION OF UNCERTAINTY

Preschool: Much More Than You Wanted To Know

I.

A lot of people pushed back against my post on preschool, so it looks like we need to discuss this in more depth.

A quick refresher: good randomized controlled trials have shown that preschools do not improve test scores in a lasting way. Sometimes test scores go up a little bit, but these effects disappear after a year or two of regular schooling. However, early RCTs of intensive “wrap-around” preschools like the Perry Preschool Program and the Abecedarians found that graduates of those programs went on to have markedly better adult outcomes, including higher school graduation rates, more college attendance, less crime, and better jobs. But these studies were done in the 60s, before people invented being responsible, and had kind of haphazard randomization and followup. They were also small sample sizes, and from programs that were more intense than any of the scaled-up versions that replaced them. Modern scaled-up preschools like Head Start would love to be able to claim their mantle and boast similar results. But the only good RCT of Head Start, the HSIS study, is still in its first few years. It’s confirmed that Head Start test score gains fade out. But it hasn’t been long enough to study whether there are later effects on life outcomes. We can expect those results in ten years or so. For now, all we have is speculation based on a few quasi-experiments.

Deming 2009 is my favorite of these. He looks at the National Longitudinal Survey of Youth, a big nationwide survey that gets used for a lot of social science research, and picks out children who went to Head Start. These children are mostly disadvantaged because Head Start is aimed at the poor, so it would be unfair to compare them to the average child. He’s also too smart to just “control for income”, because he knows that’s not good enough. Instead, he finds children who went to Head Start but who have siblings who didn’t, and uses the sibling as a matched control for the Head Starter.

This ensures the controls will come from the same socioeconomic stratum, but he acknowledges it raises problems of its own. Why would a parent send one child to Head Start but not another? It might be that one child is very stupid and so the parents think they need the extra help preschool can provide; if this were true, it would mean Head Starters are systematically dumber than controls, and would underestimate the effect of Head Start. Or it might be that one child is very smart and the so the parents want to give them education so they can develop their full potential; if this were true, it would mean Head Starters are systematically smarter than controls, and would inflate the effect of Head Start. Or it might be that parents love one of their children more and put more effort into supporting them; if this meant these children got other advantages, it would again inflate the effect of Head Start. Or it might mean that parents send the child they love more to a fancy private preschool, and the child they love less gets stuck in Head Start, ie the government program for the disadvantaged. Or it might be that parents start out poor, send their child to Head Start, and then get richer and send their next child to a fancy private preschool, while that child also benefits from their new wealth in other ways. There are a lot of possible problems here.

Deming tries very hard to prove none of these are true. He compares Head Starters and their control siblings on thirty different pre-study variables, including family income during their preschool years, standardized test scores, various measures of health, number of hours mother works during their preschool years, breastfedness, etc. Of these thirty variables, he finds a significant difference on only one: birth weight. Head Starters were less likely to have very low birth weight than their control siblings. This is a moderately big deal, since birth weight is a strong predictor of general child health and later life success. But:

Given the emerging literature on the connection between birth weight and later outcomes, this is a serious threat to the validity of the [study]. There are a few reasons to believe that the birth weight differences are not a serious source of bias, however. First, it appears that the difference is caused by a disproportionate number of low-birth-weight children, rather than by a uniform rightward shift in the distribution of birth weight for Head Start children. For example, there are no significant differences in birth weight once low-birth-weight children (who represent less than 10 percent of the sample) are excluded.

Second, there is an important interaction between birth order and birth weight in this sample. Most of the difference in mean birth weight comes from children who are born third, fourth, or later. Later-birth-order children who subsequently enroll in Head Start are much less likely to be low birth weight than their older siblings who did not enroll in preschool. When I restrict the analysis to sibling pairs only, birth weight differences are much smaller and no longer significant, and the main results are unaffected. Finally, I estimate all the models in Section V with low-birth-weight children excluded, and, again, the main results are unchanged.

Still, to get a sense of the magnitude of any possible positive bias, I back out a correction using the long-run effect of birth weight on outcomes estimated by Black, Devereux, and Salvanes (2007). Specifically, they find that 10 percent higher birth weight leads to an increase in the probability of high school graduation of 0.9 percentage points for twins and 0.4 percentage points for siblings. If that reduced form relationship holds here, a simple correction suggests that the effect of Head Start on high school graduation (and by extension, other outcomes) could be biased upward by between 0.2 and 0.4 percentage points, or about 2–5 percent of the total effect.

Having set up his experimental and control group, Deming does the study and determines how well the Head Starters do compared to their controls. The test scores show some confusing patterns that differ by subgroup. Black children (the majority of this sample; Head Start is aimed at disadvantaged people in general and sometimes at blacks in particular) show the classic pattern of slightly higher test scores in kindergarten and first grade, fading out after a few years. White children never see any test score increases at all. Some subgroups, including boys and children of high-IQ mothers, see test score increases that don’t seem to fade out. But these differences in significance are not themselves significant and it might just be chance. Plausibly the results for blacks, who are the majority of the sample, are the real results, and everything else is noise added on. This is what non-subgroup analysis of the whole sample shows, and it’s how the study seems to treat it.

The nontest results are more impressive. Head Starters are about 8% more likely to graduate high school than controls. This pattern is significant for blacks, boys, and children of low-IQ mothers, but not for whites, girls, and children of high-IQ mothers. Since the former three categories are the sorts of people at high risk of dropping out of high school, this is probably just floor effects. Head Starters are also less likely to be diagnosed with a learning disability (remember, learning disability diagnosis is terrible and tends to just randomly hit underperforming students), and marginally less likely to repeat grades. The subgroup results tend to show higher significance levels for groups at risk of having bad outcomes, and lower significance levels for the rest, just as you would predict. There is no effect on crime. For some reason he does not analyze income, even though his dataset should be able to do that.

He combines all of this into an artificial index of “young adult outcomes” and finds that Head Start adds 0.23 SD. You may notice this is less than the 0.3 SD effect size of antidepressants that everyone wants to dismiss as meaningless, but in the social sciences apparently this is pretty good. Deming optimistically sums this up as “closing one-third of the gap between children with median and bottom-quartile family income”, as “75% of the black-white gap”, and as “80% of the benefits of [Perry Preschool] at 60% of the cost”.

Finally, he does some robustness checks to make sure this is not too dependent on any particular factor of his analysis. I won’t go into these in detail, but you can find them on page 127 of the manuscript, and it’s encouraging that he tries this, given that I’m used to reading papers by social psychologists who treat robustness checks the way vampires treat garlic.

Deming’s paper very similar to Garces Thomas & Currie (2002), which does the same methodology on a different dataset. GTC is earlier and more famous and probably the paper you’ll hear about if you read other discussions of this topic; I’m focusing on Deming because I think his analyses are more careful and he explains what he’s doing a lot better. Reading between the lines, GTC do not find any significant effects for the sample as a whole. In subgroup analyses, they find Head Start makes whites more likely to graduate high school and attend college, and blacks less likely to be involved in crime. One can almost sort of attribute this to floor effects; blacks many times more likely to have contact with the criminal justice system, and there are more blacks than whites in the sample, so maybe it makes sense that this is only significant for them. On the other hand, when I look at the results, there was almost as strong a positive effect for whites (ie Head Start whites committed more crimes, to the same degree Head Start blacks committed fewer crimes) – but there were fewer whites so it didn’t quite reach significance. And the high school results don’t make a lot of sense however you parse them. GTC use the words “statistically significant” a few times, so you know they’re thinking about it. But they don’t ever give significance levels for individual results and one gets the feeling they’re not very impressive. Their pattern of results isn’t really that similar to Deming’s either – remember, Deming found that all races were more likely to benefit from high school, and no race had less crime. GTC also don’t do nearly as much work to show that there aren’t differences between siblings. Deming is billed as confirming or replicating GTC, but this only seems true in the sense that both of them say nice things about Head Start. Their patterns of results are pretty different, and GTC’s are kind of implausible.

And for that matter, ten years earlier two of these authors, Currie and Thomas, did a similar study. They also use the National Longitudinal Survey of Youth, meaning I’m not really clear how their analysis differs from Deming’s (maybe it’s much earlier and so there’s less data?) They first use an “adjust for confounders” model and it doesn’t work very well. Then they try a comparing-siblings model and find that Head Starters are generally older than their no-preschool siblings, and also generally born to poorer mothers (these are probably just the same result; mothers get less poor as they get older). They also tend to do better on a standardized test, though the study is very unclear about when they’re giving this test so I can’t tell if they’re saying that group assignment is nonrandom or that the intervention increased test scores. They find Head Start does not increase income, maybe inconsistently increases test scores among whites but not blacks, decreases grade repetition for whites but not blacks, and improves health among blacks but not whites. They also look into Head Start’s effect on mothers, since part of the wrap-around program involves parent training. All they find is mild effects on white IQ scores, plus “a positive and implausibly large effect of Head Start on the probability that a white mother was a teen at the first birth” which they say is probably sampling error. Like the later study, this study does not give p-values and I am too lazy to calculate them from the things they do give, but it doesn’t seem like they’re likely to be very good.

Finally, Deming’s work was also replicated and extended by a team from the Brookings Institute. I think what they’re doing is taking the National Longitudinal Survey of Youth – the same dataset Deming and one of the GTC papers used – and updating it after a few more years of data. Like Deming, they find that “a wide variety” of confounders do not differ between Head Starters and their unpreschooled siblings. Because they’re with the Brookings Institute, their results are presented in a much prettier way than anyone else’s:

The Brookings replication (marked THP here) finds sizes somewhat larger than GTC, but somewhat smaller than Perry Preschool. It looks like they find a positive and significant effect on high school graduation for Hispanics, but not blacks or whites, which is a different weird racial pattern than all the previous weird racial patterns. Since their sample was disproportionately black and Hispanic, and the blacks almost reached significance, the whole sample is significant. They find increases of about 6% on high school graduation rates, compared to Deming’s claimed 8%, but on this chart it’s hard to see how Deming said his 8% was 80% as good as Perry Preschool. There are broadly similar effects on some other things like college attendance, self esteem, and “positive parenting”. They conclude:

These results are very similar to those by Deming (2009), who calculated high school graduation rates on the more limited cohorts that were available when he conducted his work.

These four studies – Deming, GTC, CT, and Brookings – all try to do basically the same thing, though with different datasets. Their results all sound the same at the broad level – “improved outcomes like high school graduation for some racial groups” – but on the more detailed level they can’t really agree which outcomes improve and which racial groups they improve for. I’m not sure how embarrassing this should be for them. All of their results seem to be kind of on the border of significance, and occasionally going below that border and occasionally above it, which helps explain the contradictions while also being kind of embarrassing in and of itself (Deming’s paper is the exception, with several results significant at the 0.01 level). Most of them do find things generally going the right direction and generally sane-looking findings. Overall I feel like Deming looks pretty good, the Brookings replication is too underspecified for me to have strong opinions on, and the various GTC papers neither add nor subtract much from this.

II.

I’m treating Ludwig and Miller separately because it’s a different – and more interesting – design.

In 1965, the government started an initiative to create Head Start programs in the 300 poorest counties in the US. There was no similar attempt to help counties #301 and above, so there’s a natural discontinuity at county #300. This is the classic sort of case where you can do a regression discontinuity experiment, so Ludwig and Miller decided to look into it and see if there was some big jump in child outcomes as you moved from the 301st-poorest-county to the 300th.

They started by looking into health outcomes, and found a dramatic jump. Head Start appears to improve the outcomes of certain easily-preventable childhood diseases 33-50%. For example, kids from counties with Head Start programs had much less anemia. Part of the Head Start program is screening for anemia and supplementing children with iron, which treats many anemias. So this is very unsurprising. Remember that the three hundred poorest counties in 1965 were basically all majority-black counties in the Deep South and much worse along every axis than you would probably expect – we are talking near-Third-World levels of poverty here. If you deploy health screening and intervention into near-Third-World levels of poverty, then the rates of easily preventable diseases should go down. Ludwig and Miller find they do. This is encouraging, but not really surprising, and maybe not super-relevant to the rest of what we’re talking about here.

But they also find a “positive discontinuity” in high school completion of about 5%. Kids in the 300th-and-below-poorest counties were about 5% more likely than kids in the 301st-and-above-poorest to finish high school. This corresponds to an average of staying in school six months longer. This discontinuity did not exist before Head Start was set up, and it does not exist among children who were the wrong age to participate in Head Start at the time it was set up. It comes into existence just when Head Start is set up, among the children who were in Head Start. This is a pretty great finding.

Unfortunately, it looks like this. The authors freely admit this is just at the limit of what they can detect at p < 0.05 in their data. They double check with another data source, which shows the same trend but is only significant at p < 0.1. "Our evidence for positive Head Start impacts on educational attainment is more suggestive, and limited by the fact that neither of the data sources available to us is quite ideal." This study has the strongest design, and it does find an effect, but the effect is basically squinting at a graph and saying "it kind of looks like that line might be a little higher than the other one". They do some statistics, but they are all the statistical equivalent of squinting at the graph and saying "it kind of looks like that line might be a little higher than the other one", and about as convincing. For a more complete critical look, see this post from the subreddit.

There is one other slightly similar regression discontinuity study, Carneiro and Ginja, which regresses a sample of people on Head Start availability and tries to prove that people who went to Head Start because they were just within the availability cutoff do better than people who missed out on Head Start because they were just outside it. This sounds clever and should be pretty credible. They find a bunch of interesting effects like that Head Starters are less likely to be obese, and less likely to be depressed. They find that non-blacks (but not blacks) are less likely to be involved in crime (which, remember, is the opposite finding as the last paper about Head Start and crime and race). But they don’t find any effect on likelihood to graduate high school or be involved in college. Also, they bury this result and everyone cites this paper as “Look, they’ve replicated that Head Start works!”

III.

A few scattered other studies to put these in context:

In 1980, Chicago created “Child Parent Centers”, a preschool program aimed at the disadvantaged much like all of these others we’ve been talking about. They did a study, which for some reason published its results in a medical journal, and which doesn’t really seem to be trying in the same way as the others. For example, it really doesn’t say much about the control group except that it was “matched”. Taking advantage of their unusually large sample size and excellent follow-up, they find that their program made children stay in school the same six months longer as many of the other studies find, had a strong effect on college completion (8% vs. 14% of kids), showed dose-dependent effects, and “was robust”. They are bad enough at showing their work that I am forced to trust them and the Journal of the American Medical Association, a prestigious journal that I can only hope would not have published random crap.

Havnes and Mogstad analyze a free universal child-care program in Norway, which was rolled out in different places at different times. They find that “exposure to child care raised the chances of completing high school and attending college, in orders of magnitude similar to the black-white race gaps in the US”. I am getting just cynical enough to predict that if Norway had black people, they would have a completely different pattern of benefits and losses from this program, but the Norwegians were able to avoid a subgroup analysis by being a nearly-monoethnic country. This is in contrast to Quebec, where a similar childcare program seems to have caused worse long-term outcomes. Going deeper into these results supports (though weakly and informally) a model where, when daycare is higher-quality than parental care, child outcomes improve; when daycare is lower-quality than parental care, child outcomes decline. So a reform that creates very good daycare, and mostly attracts children whose parents would not be able to care for them very well, will be helpful. Reforms that create low-quality daycare and draw from households that are already doing well will be harmful. See the discussion here.

Then there’s Chetty’s work on kindergarten, which I talk about here. He finds good kindergarten teachers do not consistently affect test scores, but do consistently affect adult earnings, similar to fade-out arguments around preschool. This study is randomized and strong. Its applicability to the current discussion is questionable, since kindergarten is not preschool, having a good teacher is not going to preschool at all, and the studies we’re looking at mostly haven’t found results about adult earnings. At best this suggests that schooling can have surprisingly large and fading-out-then-in-again effects on later life outcomes.

And finally, there’s a meta-analysis of 22 studies of early childhood education showing an effect size of 0.24 SD in favor of graduating high school, p less than 0.001. Maybe I should have started with that one. Maybe it’s crazy of me to save this for the end. Maybe this should count for about five times as much as everything I’ve mentioned so far. I’m putting it down here both to inflict upon you the annoyance I felt when discovering this towards the end of researching this topic, and so that you have a good idea of what kind of studies are going into this meta-analysis.

IV.

What do we make of this?

I am concerned that all of the studies in Parts I and II have been summed up as “Head Start works!”, and therefore as replicating each other, since the last study found “Head Start works!” and so did the newest one. In fact, they all find Head Start having small effects for some specific subgroup on some specific outcome, and it’s usually a different subgroup and outcome for each. So although GCT and Deming are usually considered replications of each other, they actually disprove each other’s results. One of GCT’s two big findings is that Head Start decreases crime among black children. But Deming finds that Head Start had no effect on crime among black children. The only thing the two of them agree on is that Head Start seems to improve high school graduation among whites. But Carneiro and Ginja, which is generally thought of as replicating the earlier two, finds Head Start has no effect on high school graduation among whites.

There’s an innocent explanation here, which is that everyone was very close to the significance threshold, so these are just picking up noise. This might make more sense graphically:

It’s easy to see here that both studies found basically the same thing, minus a little noise, but that Study 1 has to report its results as “significant for blacks but not whites” and Study 2 has to report the opposite. Is this what’s going on?

I made a table. I am really really not confident in this table. On one level, I am fundamentally not confident that what I am doing is even possible, and that the numbers in these studies are comparable to one another or mean what it looks like they mean. On a second level, I’m not sure I recorded this information correctly or put the right numbers in the right places. Still, here is the table; red means the result is significant:

This confirms my suspicions. Every study found something different, and it isn’t even close. For example, Carneiro & Ginja finds a strong effect of lowering white crime, but GCT finds that Head Start nonsignificantly increases white crime rates. Meanwhile, GCT find a strong and significant effect lowering black crime, but Carneiro and Ginja find an effect of basically zero.

The strongest case for the studies being in accord is for black high school graduation rates. Both Deming and Ludwig+Miller find an effect. Carneiro and Ginja don’t find an effect, but their effect size is similar to those of the other studies, and they might just have more stringent criteria since they are adjusting for multiple comparisons and testing many things. But they should have the more stringent criteria, and by trying to special-plead against this, I am just reversing the absolutely correct thing they did because I want to force positive results in the exact way that good statistical practice is trying to prevent me from doing. So maybe I shouldn’t do that.

Here is the strongest case for accepting this body research anyway. It doesn’t quite look like publication bias. For one thing, Ludwig and Miller have a paper where they say there’s probably no publication bias here because literally every dataset that can be used to test Head Start has been. For another, although I didn’t focus on gender or IQ on the chart above, most of the studies do find that it helps males and low-IQ people more with the sorts of problems men and low-IQ people usually face, which suggest it passes sanity checks. Most important, in a study whose results are entirely spurious, there should be an equal number of beneficial and harmful findings (ie they should find Head Start makes some subgroups worse on some outcomes). Since each of these studies investigates many things and usually finds many different significant results, it should be hard to publication bias all harmful findings out of existence. This sort of accords with the positive meta-analysis. Studies either show small positive results or are not signficant, and when you combine all of them into a meta-analysis, they become highly significant, look good, and make sense. And this would fit very well with the Norwegian study showing strong positive effects of childcare later in life. And Chetty’s study showing fade-out of kindergarten teachers followed by strong positive effects later in life. And of course the Perry Preschool and Abecedarian studies showing fade-out of tests scores followed by strong positive effects later in life. I even recently learned of a truly marvelous developmental explanation for why this might happen, which unfortunately this margin is too small to contain – expect a book review in the coming weeks.

The case against this research is that maybe the researchers cheated to have there be no harmful findings. Maybe the meta-analysis just shows that when a lot of researchers cheat a little, taking care to only commit minor undetectable sins, that adds up to a strong overall effect. This is harsh, but I was recently referred to this chart (h/t Mother Jones, which calls it “the chart of the decade” and “one of the greatest charts ever produced”):

This is the outcome of drug trials before and after the medical establishment started requiring preregistration (the vertical line) – in other words, before they made it harder to cheat. Before the vertical line, 60% of trials showed the drug in question was beneficial. After the vertical line, only 10% did. In other words, making it harder to cheat cuts the number of positive trials by a factor of six. It is not at all hard to cheat in the research of early childhood education; all the research in this post so far comes from the left side of the vertical line. We should be skeptical of all but the most ironclad research that comes from the left – and this is not the most ironclad research.

The Virtues of Rationality say:

One who wishes to believe says, “Does the evidence permit me to believe?” One who wishes to disbelieve asks, “Does the evidence force me to believe?” Beware lest you place huge burdens of proof only on propositions you dislike, and then defend yourself by saying: “But it is good to be skeptical.” If you attend only to favorable evidence, picking and choosing from your gathered data, then the more data you gather, the less you know. If you are selective about which arguments you inspect for flaws, or how hard you inspect for flaws, then every flaw you learn how to detect makes you that much stupider.

This is one of the many problems where the evidence permits me to disbelieve, but does not force me to do so. At this point I have only intuition and vague heuristics. My intuition tells me that in twenty years, when all the results are in, I expect early childhood programs to continue having small positive effects. My vague heuristics say the opposite, that I can’t trust research this irregular. So I don’t know.

I think I was right to register that my previous belief preschool definitely didn’t work was outdated and under challenge. I think I was probably premature to say I was wrong about preschool not working; I should have said I might be wrong. If I had to bet on it, I would say 60% odds preschool helps in ways kind of like the ones these studies suggest, 40% odds it’s useless.

I hope that further followup of the HSIS, an unusually good randomized controlled trial of Head Start, will shed more light on this after its participants reach high school age sometime in the 2020s.

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164 Responses to Preschool: Much More Than You Wanted To Know

  1. Radu Floricica says:

    > I would say 60% odds preschool helps in ways kind of like the ones these studies suggest

    But… costs. In the end, betting that years of effort help “somewhat” is really “duh” territory. Are they even close to recouping costs, including opportunity ones?

    • brmic says:

      Are they even close to recouping costs, including opportunity ones?

      Are you seriously interested in this question or are you using it to avoid engaging with the evidence and to reinforce your prior?

      I submit that a useful way to distinguish the two would be whether you made a serious effort to find out whether that question is addressed in the literature.

      • untimelyreflections says:

        > Are you seriously interested in this question

        Government spending is full of programs that may have a benefit but where the costs outweigh the benefits. I don’t see why someone needs to justify asking what is the cost benefit.

        This is even before noting (per SSC) that these studies were not pre-registered. So discount by a factor of 6. They had so many degrees of freedom that the reported P values are almost certainly exaggerated.

        And a meta-analysis based on cherry picked stats is also highly suspect.

        • brmic says:

          I don’t see why someone needs to justify asking what is the cost benefit.

          They do, when they raise the question as an objection, i.e. pretend to care about this, as in, pretend it is relevant to their overall take on the matter while apparently having spent so little time on the question that they can’t even reach a tentative conclusion on it’s factual state.
          If it was a totally neutral query, sure, that’s perfectly legit, but that’s not what the comment was.

          As for pre-registration and the meta-analysis, did you miss the part where Scott said that both every outcome and every conceivable dataset had been looked at in the context of these interventions? (Also, FWIW, if you take the factor 6 from the post above, I think that’s a misinterpretation of the cited paper by Scott based on the poor discussion in the paper. I’d love to discuss Likelihood of Null Effects of Large Clinical trials (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0132382) in the next OT, but think it would be a distraction here.)

          • Jack Lecter says:

            also @brmic:

            apparently having spent so little time on the question that they can’t even reach a tentative conclusion on it’s factual state… If it was a totally neutral query, sure, that’s perfectly legit, but that’s not what the comment was.

            I don’t usually find a lack of knowledge to be evidence against neutrality.

            What’s the ninth largest country by landmass divided by population? I have no idea, largely because I don’t really care. If you said it was Antarctica, though, I’d be dubious, just on priors.

            I think what you’re talking about is a real thing, but I don’t see a lot of reason to think that’s what’s happening here.

            At a mild tangent: my prior is that people often forget to weigh all the advantages and disadvantages, and that taxes are sometimes a particularly fertile area for this. I think my natural inclination is to be pro-schooling- it benefits kids, it seems like it might get us a more rational population- but when I see an article about whether we should be doing it or not that makes no mention of costs, alarms go off. It’s half legitimate quibble, half local validity thing.

          • Randy M says:

            If it was a totally neutral query, sure, that’s perfectly legit, but that’s not what the comment was.

            I don’t really care who raises the question of cost, or for what motive, but I am happy that someone does so between suggesting a policy and deciding if it is worth doing.

      • jasmith79 says:

        This seems unnecessarily argumentative. I believe what he’s saying is that even if you charitably accede that the research is correct in showing a small positive net benefit on outcomes that it is still probably not worth it vs. e.g. simply giving the parents money, or even possibly doing nothing at all. I’m unsure what “avoid(ing) engaging with the evidence” could add or subtract here.

        • brmic says:

          It would add _at the very least_ the requirement that you check the papers linked for whether any of them addresses the question.
          You’re doing the same thing without noticing it here: ‘probably not worth it’. You don’t know, you haven’t run the numbers, you don’t even have a position on someone else’s report of having run the numbers. You just moved your bias one level up.
          This is very bad epistemiology for a rationalist comment section.

          As mentioned above, I think it’s fine to ask a truly open question. It’s fine to disagree with the available analyses, to find fault with them, to point to other analyses with different results. But if you haven’t done an analysis, and haven’t read one and still assert what it’s outcome would likely be, you’re using your biases, not your ratio to come to that conclusion.

          • lazydragonboy says:

            But if you haven’t done an analysis, and haven’t read one and still assert what it’s outcome would likely be, you’re using your biases, not your ratio to come to that conclusion

            Reading through the thread, I wasn’t really with you until this line. I didn’t especially disagree with you either, but I wasn’t fully persuaded. More that I sort of got what you were getting at, but some of the critiques levied against your position seemed valid too.

            But this is a really good point. The manner of delivery indicates biased skepticism in a way that you have very elegantly explicated; hats off to you.

          • jasmith79 says:

            Ok, I get where you’re coming from now. I concede the general point. In this specific case, we’re talking about a massive federal program. My wife and I both work in government (she in social services) and I (in rationalist parlance) have a high prior that unless this program provides a significant benefit it couldn’t possibly justify the cost of its existence (although, again, as a rationalist I’m open to the idea of the data saying otherwise).

      • Jack Lecter says:

        @brmic:

        I submit that a useful way to distinguish the two would be whether you made a serious effort to find out whether that question is addressed in the literature.

        In his defense, asking Scott has proven to be a reliable low-effort alternative to looking things up. I kind of had the same question, tbh.

        I think there are a lot of things I care enough about to ask a smart friend, but not enough about to research them on my own.

        The utility of looking for yourself varies a lot, at least mine does; if I expect to find the answer on my own, it’s often worth it, but if there’s just a hole where the answer should be… then there’s never a clear point where it’s time to stop looking, which is stressful, and ever after I wonder if I should have looked longer.

        • Paul Zrimsek says:

          That approach particularly suggests itself when you’re commenting on a post in which Scott bemoans the difficulty of wringing out of the literature even a tentative conclusion about whether the programs produce any benefit at all. If the studies point every which way on that question, it would be surprising if they gave a definitive answer on cost vs. benefit.

      • JohnBuridan says:

        In Radu’s defense, at the end of the previous post on Preschool Scott made a policy recommendation. But since, Scott did not revisit that recommendation here I read it as a legitimate question part of the larger conversation we are having about preschool.

        There is no rule here that every comment has to be a comment directly related to the OP.

        On the other hand, Radu’s post comes across as needlessly inflammatory and low-effort ‘whataboutism.’

    • Mr. Doolittle says:

      One identified intervention that makes a lot of sense (at least in the 1960s) was basic medical screening. That’s gotta be a whole lot cheaper than daily care and teaching, and would cover one of the strongest results from any of the studies.

    • Guy in TN says:

      But they are two entirely different questions. “Does preschool help kids?” vs. “Is the cost of preschool worth it?”

      The post is long enough as it is. And answering the second question would require a deep-dive into economic and political philosophy. Questions of taxation, political feasibility, and weighing moral values against each other.

      It’s better just to answer the first, smaller question, and use the results to update whatever preexisting political philosophy you have.

      • j r says:

        The post is long enough as it is. And answering the second question would require a deep-dive into economic and political philosophy. Questions of taxation, political feasibility, and weighing moral values against each other.

        That’s true if you are trying to evaluate whether it’s better to spend an extra dollar on preschool or lower taxes by a dollar. But it’s not so true if you’re trying to decide whether to spend a dollar on preschool or a give a dollar cash transfer or spend a dollar on some health intervention or spend a dollar improving public high schools.

        Most of these objections to Radu’s question imply that questioning the efficacy of preschool is some kind of de facto red tribe position. It can be. And it can be something entirely different. For one thing, one of the reasons that universal preschool has such widespread political support is that people tend to view children as innocent and, therefore, want to believe that they ultimately malleable.

        It can sometimes be much easier to get people to approve of public programs aimed at very young children than to support interventions for older children, in part, because people tend to believe that older children have already made their choices and are irredeemable. Personally, I think it is worth the time and effort to find out how true these assumptions really are.

    • Scott Alexander says:

      What you’re calling “duh territory” is what I said I can only be 60% sure of at this point, and what many commenters on the last post denied entirely. I think your intuitions here are different from other people’s.

      Many of the studies I linked, including Deming, included cost-benefit analyses purporting to show that benefits exceeded costs at the effect sizes they found. I wasn’t as interested in these because I am more focused on the academic question of what affects early childhood development, but you can take a look at them if you want.

    • Yosarian2 says:

      If the results are correct, and it inceases high school graduation rates by 8%, then it’s worth the cost just from that alone.

      https://www.ssa.gov/retirementpolicy/research/education-earnings.html

      High school graduates earn about $400,000 more over a lifetime than people who don’t finish high school. 8% of that is $36,000 per student. Head start only costs about $7600 per student.

      There are a lot of other likely benefits here as well, lower crime rate is also a big deal, poor parents probably earn more if they have child care, ect. If you agree there’s a 60% chance it raises high school graduation rates and a 60% chance it reduces crime it’s a good investment.

      • baconbits9 says:

        Head start costs that up front though, $7,600 compounded for 65 years at 5% is $180,000 and at 7% is $620,000

      • Paul Zrimsek says:

        That may be overstating the benefit. Assume that Head Start achieves its result by turning marginal dropouts into marginal graduates: marginal dropouts probably earn more on average than the entire population of dropouts, while marginal graduates probably earn less on average than the entire population of graduates.

        • John Schilling says:

          True, but Head Start presumably also turns median dropouts into superior dropouts, and marginal graduates into median graduates, which will both be associated with some increase in earning potential. Very roughly speaking, an 8% increase in graduation rates means that everybody moves up an average of 8% of the “distance” between zero and minimal high school graduation

          If you can’t measure at that level of detail, assuming that a flat 8% (or whatever) jump directly from “average dropout” to “average graduate” is a statistically reasonable approximation of the full effect; assuming that the benefit was only experienced by the top 8% of dropouts is not.

          But, accounting for the time value of money, Head Start is still looking like a very marginal proposition and we should also be looking at other things we could be doing better.

          • uau says:

            As the article says, “These children are mostly disadvantaged because Head Start is aimed at the poor”. I don’t think “average dropout” to “average graduate” is a reasonable assumption for such selected population; “average dropout” to “minimal graduate” seems like a better starting assumption (high end of graduates is still going to be rare even after the program).

          • Paul Zrimsek says:

            The possibility being suggested, if I’m understanding it right, isn’t that the average dropouts get upgraded directly to average grads– it’s that they slide over to take the place of the somewhat-better-than-average dropouts, who in turn take the place of the just-missed-graduating, and so on up the chain, so that the net effect is the same as if the people at the bottom end leapfrogged to the top while everyone else stood still. It’s possible, though speculative (we’re no longer talking about a direct benefit from increased graduation rates, but rather using the increase as a proxy for benefits to people whose graduation status hasn’t changed).

            One detail I missed at first which adds a bit of plausibility to the case for preschool: the $400,000 improvement in earnings is based on the median for high-school graduates with no further educational attainment— not for all high-school graduates. That’s a more reasonable example of something current dropouts might aspire to with a bit of help.

          • uau says:

            @Paul Zrimsek:
            But the studies didn’t say that academic performance would improve noticeably, so I assume it’s just that people choose to continue education even though they aren’t doing particularly well. This effect clearly produces more low-quality graduates.

            Even if you assumed that academic performance or even IQ were boosted directly, if the shapes of the distributions for the poor population and others were anything like normal distributions, boosting the inferior population to a better-but-still-inferior level would still increase the graduates proportionally more at the worse-than-average level.

      • DeservingPorcupine says:

        Individual return isn’t the same as social return.

    • Alkatyn says:

      The child not being at preschool also has significant oppurtunity costs, since the alternative is normally one parent being at home with them and not working. So even if the value of preschool for the child is negligible it can be beneficial through higher parental earnings (both during the time they’re in preschool and in the future from better job experience). Which is good for the family as a whole, and probably for the child given all the well known positive outcomes of more money

  2. toastengineer says:

    You should probably alter this line:

    We should be skeptical of all but the most ironclad research that comes from the left – and this is not the most ironclad research.

    before someone takes it out of context.

  3. Hmm…still skeptical.

    Okay let’s assume head start and preschool produce tiny but statistically significant later gains in life among some blacks and maybe some Hispanics. Is it worth the cost. If slightly boosting high school or college attendance is considered a success, then there are probably cheaper and more effective ways of doing that (such as giving high school grads $10 to apply to college). It sorta seems like goalpost moving: your program fails to do what it was originally intended, but because there are are some tiny secondary gains later in life if one looks hard enough, that justifies keeping the program. It’s like saying the Iraq war failed to find anything or create peace and it cost trillions of dollars, but because it boosted the sale of patriotic bumper stickers, it is worthwhile.

    • Jade North says:

      In fact, the goalposts were moved for the Iraq War. The original impetus was to protect the US from weapons of mass destruction. After we sent in the military, wasted pallets of cash, and discovered no weapons of mass destruction, we patted ourselves on the back for freeing the Iraqi people from a dictator. Would we have spent so many lives and resources if the original goal was to depose a dictator? Assuredly not.

      • Ghillie Dhu says:

        I’m not sure conflating the public justification(s) for the war with the actual impetus is justified.

        Similarly, I am skeptical that the arguments for programs like Head Start are causally-related to the objectives of proponents.

      • cassander says:

        In fact, the goalposts were moved for the Iraq War. The original impetus was to protect the US from weapons of mass destruction.

        This is inaccurate. that was, at most, the most noisy justification of the war. the goal, and virtually every book written on the bush administration agrees with this point, was to get rid of nasty despots in the middle east and replace them with democracies in order to drain the swamp of terrorism. And this goal was achieved, to a remarkable degree. It took several years longer, and about a trillion dollars more, than was originally anticipated, but it was achieved.

        • acymetric says:

          Yes, the middle-east is a bastion of America loving democracies now…mission accomplished.

          Also, that may have been the administration’s goal, but that is not how it was presented or justified to the public.

          • cassander says:

            >Yes, the middle-east is a bastion of America loving democracies now…mission accomplished.

            They didn’t do the whole middle east. they did iraq. And Iraq is a democracy, the only one in the arab world.

            >Also, that may have been the administration’s goal, but that is not how it was presented or justified to the public.

            Yes, it was. WMD was only one of many arguments explicitly articulated by the administration, one that feels louder in hindsight than it actually was becuase of the unexpected failure to find any meant that critics could hammer them on the point.

          • idontknow131647093 says:

            Cass, I am a bit young to fully remember the political debates about whether we should have gone into Iraq, but my memory is that WMD was reason #1 and reason #2 was a distant second.

            If this wasn’t the case, then there is a real problem with the military strategy for the war. People love to tout “the surge” etc at the end of the Bush years, but if you wanted democracy, you needed to not just take out Saddam and the Royal Guard, you needed to take POWs and keep them encamped for a few years, you needed to bomb “strategic locations” in cities (aka any plausible target you can find without explicitly admitting you are committing a war crime) and start from day 1 with a robust propaganda and iron first (aka counterinsurgency) campaign.

          • acymetric says:

            The article you linked seems to imply that WMD was indeed the primary (but not only) argument going into the war, but then subsided as evidence that WMDs were there subsided. I feel like this detracts from your point rather than supports it.

          • j r says:

            I second what acymetric said. This was the face of the administration’s case for the Iraq War: https://en.wikipedia.org/wiki/United_Nations_Security_Council_and_the_Iraq_War#Colin_Powell's_presentation

            Of course they downplayed the WMD angle and Iraq’s role in supporting terror and tried to shift focus to democratization as the first two proved… elusive.

            Also, I would take a closer look at Iraq’s current democracy and then ask some serious cost-benefit questions before declaring the Iraq War a success.

          • bean says:

            It’s also worth pointing out that everyone believed that Iraq did have WMDs. Including Saddam, probably. If he didn’t have the things, why did he play games with the UN weapons inspectors? Maybe he wanted us to believe he did, but at this point, all you’re saying is that he fooled the CIA. Which isn’t impossible.

          • Protagoras says:

            @bean, The easy explanation for why he played games with the weapons inspectors is that he wanted his local rivals to believe he had WMDs.

          • cassander says:

            idontknow131647093

            If this wasn’t the case, then there is a real problem with the military strategy for the war.

            Their strategy was to pull a massive scale version of the invasion of grenada. the thinking was that the best way to prevent an insurgency was to get in and out as quickly as possible with as little an occupation as possible. It clearly didn’t work, and I’m much more inclined to the method that you describe, but that was the plan.

            @acymetric

            the evidence they present shows that in the beginning the two biggest reasons for the invasion were WMD and internationalism, with internationalism slightly more important. Both those arguments start to decline in importance before the start of the invasion, at about the same time the freedom/democracy argument starts its upwards trajectory. the WMD argument drops out long before it’s apparent that there were none.

            @Protagoras

            I tend to agree with you. the best place for saddam to be was to not have any WMD, because then no one could ever find them, but to have everyone convinced he had them, so they would all still be afraid of him.

  4. untimelyreflections says:

    Just to point out the dog that didn’t bark here – none of this affected IQ.

    The original premise was that IQ variance was environmental, but big changes to environment made no difference.

    • Robert Jones says:

      I’m a stranger to this debate, so I’m unaware of the background. What do you mean by “the original premise”?

    • Statismagician says:

      This isn’t quite right; low birth weight (proxy for general healthiness) correlates with IQ and is affected by Head Start participation; low birth weight is associated with up to 10% lower IQ, although as the authors of the linked meta-analysis note this is really hard to study in isolation. I don’t believe anybody did the kind of subset analysis which would detect this at the population level.

      • SaiNushi says:

        “low birth weight (proxy for general healthiness) correlates with IQ and is affected by Head Start participation”

        How exactly is a person’s birth weight determined by something that happened after their birth?

        Head Start did not affect the birth weight. Head Start was just disproportionately attended by kids with a low birth weight.

        • baconbits9 says:

          Head Start was just disproportionately attended by kids with a low birth weight.

          The summary said the opposite, that low birth weight kids avoided HS disproportionately.

          Of these thirty variables, he finds a significant difference on only one: birth weight. Head Starters were less likely to have very low birth weight than their control siblings.

          This is probably the most interesting point not yet discussed. I would have guess the opposite, if you had a low birth weight child with issues wouldn’t you be more aggressive in seeking out help, not less? The mechanism for selecting against low birth weight should be discussed (it also is possibly a coincidence since he looked at 30 variables and found 1 that was significant in a P-hacking sort of way).

        • Statismagician says:

          Early Head Start includes perinatal medical care and education.

  5. Robert Jones says:

    It seems very unlikely that pre-school could have an effect which was race-dependent in any fundamental way. Where there are observed differences in outcomes between racial groups that is presumably because race is a proxy for something else (like poverty), but that relationship will be inconsistent across time and space. Might that explain the inconsistent outcomes by racial subgroups? I don’t really understand why the data is being analysed in this way.

    • jasmith79 says:

      That’s a fashionable but difficult pre-supposition (that race is only a proxy for e.g. poverty).

      Maybe there are important genetic differences between races (I’m not convinced there are, but can’t rule it out a priori). Maybe the cultural impacts of racism and colonialism are strong enough that they last for generations after colonialism is dead and overt racism is rare (my hunch says yes to at least this one).

      Or maybe you’re right but it’s moot: race is a proxy for culture but the cultural influences are so pervasive that it might as well be a thing, and unlike poverty this would be more stable over time (or rather would require a longer timescale to show meaningful change).

      Or maybe your just plain right: it’s a reasonable guess. But I have a lower prior for that viewpoint than it’s popularity would suggest.

      • Jade North says:

        But race is also a proxy for cultural impacts. Nigerian immigrants from the 90s did not have ancestors that suffered from discrimination in America.

        Race is also a proxy for culture. Not all hispanics are cultural hispanics. Not all cultural hispanics are hispanic.

        Skin color is about the least likely attribute to have a direct effect on any but a very small set of outcomes, like skin cancer. While it’s among the easiest attributes to measure, wouldn’t it make sense to invest a little more effort in singling out attributes that actually matter, like poverty, genealogy, and culture?

      • jasmith79 says:

        It depends.

        How strong is the correlation? Is it like lung cancer and smoking strong? Because if it is, we might as well just talk about race like it’s a thing. If it’s not, it’s probably worth the effort to find better categorizations.

        I’m reminded of all the SSC posts on IQ. People keep wanting to talk about different kinds of intelligence, and maybe there are, but that doesn’t mean IQ isn’t a thing.

        Maybe it’s just time to pick a word that doesn’t have as much baggage. Have we loaded up “ethnicity” with negative affect yet?

    • SaiNushi says:

      They controlled for poverty in the studies, which is why they were even taken seriously.

  6. Chalid says:

    I want to gripe at you slightly for your bad habit of citing organizations instead of people; here, “h/t Mother Jones, which calls it “the chart of the decade”” instead of “h/t Kevin Drum” or if you really feel the organization is important for some reason “h/t Kevin Drum at Mother Jones.” Kevin Drum is a blogger. His opinions are not necessarily those of Mother Jones, and vice versa. There is no sense in which “Mother Jones” is calling this “the chart of the decade” – that is Kevin Drum’s opinion only.

    You can say it’s Mother Jones’ opinion if it’s in a staff editorial.

    It’s not quite the same thing but you would immediately see the problem if someone pointed at an opinion you wrote on LessWrong and attributed it to “LessWrong” instead of “Scott Alexander.”

  7. Quixote says:

    I really enjoy posts like this and find them very interesting.

  8. nameless1 says:

    But what is preschool from what age and what are the alternatives to it? I mean in my country daycare/kindergarten/preschool/whatever you want to call that thing that happens between the ages of 2 and 6, is mostly about letting women go back to the workforce after 2 years of maternity leave. And if the kids are there anyway, they might as well try to teach them something but that is kind of secondary.

    Only the last year, when they are 5 years old, called the school preparation year is where some more formal teaching takes place. It is the only year that is mandatory, the earlier not. Is this the preschool in the US sense, is this what Scott is writing about?

    What is actually being done there? Here it is stuff like improving speech and speech understanding abilities, teamwork abilities etc.

    What is the alternative to preschool in the Scott sense? Staying at home sitting on mom’s skirt until school? Sounds like bad socialization, no relationship with other kids and losing much of the workforce. Be in a kind of daycare or kindergarten but learn nothing, just play all day? Sounds like a waste of time. Why shock kids with school being totally different than daycare instead of having a gradual transition?

    So what exactly is the no preschool scenario?

    • Unirt says:

      Same here. In my country they go to school at 7, and 6 is the school-preparation year.

      I think in the US what they call pre-school is systemtically teaching things to 3 and 4-year-olds.

      What is the alternative to preschool in the Scott sense? Staying at home sitting on mom’s skirt until school? Sounds like bad socialization, no relationship with other kids and losing much of the workforce. Be in a kind of daycare or kindergarten but learn nothing, just play all day? Sounds like a waste of time.

      These are not at all agreed upon, as I understand. It may, for example, be better to learn socializing from the grown-ups, since they are the ones who actually can socialize in a polite, pro-social manner. From the other kids you can learn how to be obnoxiously selfish and break down in tantrums if something bothers you (I don’t really mean that you can’t learn anything useful from playing with other kids).

      Also, sitting on mom’s skirt feels very safe, while going to a large group of strangers can feel real unsafe (you can see how some kids desperately cling to their parents, crying and begging, when they are being dropped off at the daycare). There are suggestive differences in child cortisol levels between daycare and no daycare days, for example. Feeling safe can plausibly be connected to good life outcomes.

      Plus we cannot deny that children had plenty of relationships with other kids before daycare became widespread, so daycare is not necessary for that. I suppose the one most important benefit of daycare is letting the mothers go to work.

      Aside from that, playing all day is probably not waste of time, play is how young kids naturally learn, right?

      • Statismagician says:

        At least in mathematics, per Benezet formal education before sixth grade is completely unnecessary at best and may be actively depressing population adult outcomes. So, yeah, fractions for toddlers are probably not a great idea.

      • nameless1 says:

        Cortisol levels: well, our kid certain screams every morning that she does not want to go to kindergarten. And yet if we are on a holiday after 2 days she says she wants to. Just like how she is screaming every evening she does not want to take a bath, and then enjoys it so much she does not want to get out. So don’t know which version of her should I believe.

        She has a weird love-hate relationship with a classmate. She sometimes says he bullies her, name-calling, and yet always looking for him and wants to play together. But I know that a bit of aggressive behavior is not alien from her either (whe she is tearing at her mothers breasts at full force, it is really hard for her to stay principled and not slap her), so I asked the boys parents and yeah there were some complaints about she bullying him as well. Again don’t know what to believe.

    • rin573 says:

      In the US, most kids go to Kindergarten when they’re 5, and that’s part of the standard schooling system. Preschool is something offered before that, usually from 3-5 years of age, and is not required and generally not free. Head Start is a free preschool program for 3-5 year old children from low-income families, and there’s also a program known as Early Head Start that helps provide health and educational services for low-income kids younger than that. The no-preschool scenario for low income families usually mean that the mother or other family members (often grandparents) take care of the kid. Sometimes the kid goes to a community or church-based daycare center, but I think this is less common. In some cases, there isn’t one person who can consistently take care of the child, so kids are sent to whatever relative or community member can currently do it. So, as Scott and Kelsey have both mentioned in their articles, the effects of preschool in the US may be related to providing any kind of consistent childcare environment, as well as giving the mothers better employment options. Any formal education preschools provide is probably irrelevant.

      Also, this is a tangential point, companies in the US are only required to offer 12 weeks of maternity leave, and this is often unpaid, especially for low paying jobs. 2 years of maternity leave is unheard of there, and there are extremely few free childcare options. This may be more relevant to the first couple years of life rather than preschool, but it might give context for what the “no preschool scenario” means.

      • herculesorion says:

        “2 years of maternity leave should be the standard!” (turns around) “wait, you want to code in Ruby On Rails? What the fuck, lady, you think it’s still 2016?”

        • rin573 says:

          ????
          This is a weird reply. I wasn’t proposing that two years of maternity leave should be standard. It probably shouldn’t, though 12 wks unpaid leave probably shouldn’t either. Also, not sure that female developers are the most relevant to a discussion more focused on low income childcare options.

          FWIW, in most countries that have 2 years, a lot of women in tech and other more competitive jobs don’t take that full period. Also, US women in tech don’t tend to be the people choosing between 12 weeks unpaid leave or nothing, they generally have at least slightly better benefits provided by their employers. Tradeoffs between parental leave and ongoing training/job experience are worth talking about, but kind of a different topic of conversation.

        • nameless1 says:

          This is an elitist viewpoint, Silicon bleedin’ edge Valley. Most websites in the world are still programmed in PHP and Asp.NET. In the comfy mediocre tepid company I work at, the average company, we are considering rewriting Asp .NET web forms in ASP.NET MVC. Don’t know the exact numbers but it is like replacing 2002 tech with 2012 tech? Roughly that.

          • herculesorion says:

            An elitist viewpoint? Maybe. But it’s not especially uncommon, and it’s not something that’s being pushed by Evul Kepitelist Bosses to exploit the poor downtrodden workers.

          • acymetric says:

            Elitist was probably a bit of a loaded word to use there…but your position definitely does not apply to the majority of coding jobs available out there (which I think is what nameless1 was getting at). It might apply to the best coding jobs, but even that probably isn’t universally true.

      • nameless1 says:

        As a Euro I don’t think maternity leave is a big deal. I get job offers from the US with much higher pretax and basically 2x as much posttax pay. So if my wife was at home for unpaid instead of paid €660 per month by the state as maternity leave (our rent + utilities is €850 so it is not a lot of money) but I would earn much more, it would be the same thing.

        I admit I think mostly conservative about this: families of 2 parents + kids, pooled income, one budget, it is entirely irrelevant if the income is dad earning a lot or maternity leave or tax breaks or whatever title it has.

        Matters more for single moms, but looking my above numbers… well at least it does not encourage family breakups much.

        Another thing is really that you cannot leave a kid in a kindergarten for 9 hours. Too stressful. So one parent will have a part time, 5-6 hour job and pick them up at 15:00. Due to social, biological or whatever reasons, the typical gender role is here the old one: dad is working his ass off to make a career, mom has more just a basic job than a career because you cannot career in 5-6 hours a day.

        • baconbits9 says:

          Another thing is really that you cannot leave a kid in a kindergarten for 9 hours. Too stressful. So one parent will have a part time, 5-6 hour job and pick them up at 15:00. Due to social, biological or whatever reasons, the typical gender role is here the old one: dad is working his ass off to make a career, mom has more just a basic job than a career because you cannot career in 5-6 hours a day.

          A good number of double income families get around this by having one parent start work early and get out early and one parent start work late and get out late.

          • acymetric says:

            What do you mean by “a good number”? I suspect that a large majority of 2-income households do not have that kind of flexibility with their work hours.

          • stationarywaves says:

            You guys could just Google an empirical question like that. Most sources I just came across in 2 minutes of searching indicate that between 27 and 30 percent of workers in the United States have access to flex time. It would appear that you’re both right: “A good number of families” do get around this; while “a large majority” do not.

            As a parent, I can tell you that a lot of us address this issue by making use of after-school programs.

          • baconbits9 says:

            About half of the 2 income families that I know do this. You only need one flexible schedule, the person working 9-5 drops off and the one who works starts between 7 and 8 picks up.

          • nameless1 says:

            This is hard in an office if the office hours are 9 to 17. But this is precisely why my wife is orienting herself towards logistics. Warehouses tend to be early birds, sending trucks out at 5:00 to get into the shops before opening.

            Now there are people who get ready in 10 minutes in the morning. We are not that kind of people. More like 90 minutes with several coffees and phone browsing. And if it takes a hour to load the truck she would get up a 2:00, go to sleep at 18:00. The kind of marriage that guard sergeant had in Terry Pratchett’s Guards! Guards! mostly conducted through post-it notes.

            So dunno what exactly are going to do to be honest.

          • baconbits9 says:

            You guys could just Google an empirical question like that. Most sources I just came across in 2 minutes of searching indicate that between 27 and 30 percent of workers in the United States have access to flex time. It would appear that you’re both right: “A good number of families” do get around this; while “a large majority” do not.

            This doesn’t give us much of an answer though. What you need is for a pair of parents to have enough differences in their schedules to make pick up and drop off work, not “flexibility”. It could be that flex time is common for certain demographics where both partners have it, and then the 37% means more like 18% of households have it, or it could be common for one partner to seek it out and then up to 74% of
            (dual income) households have it.

            But flex time really doesn’t cover it, not all flex time is flexible enough, and no flex time is needed in many situations. One couple I know both work for the same large company, one is a manager in the warehouse, and is a manager in procurement. The first is at work before 6am, the other at work until 6pm, neither needs flex time to make it work.

    • SaiNushi says:

      Daycare and preschool are separated by how many formal activities there are. Preschool has a few formal activities. Daycare has informal activities.

      Not completely sure about this next bit, but I think preschool also has a higher adult-to-child ratio than daycare. Meaning more individualized attention, which has always been shown to increase outcomes for students.

  9. Argos says:

    Regarding the Mother Jones chart: I feel like their sensationalist headline is not sensationalist enough:

    Doesn’t the chart mean that we cannot trust ANY medical reasearch that came out before 2000, and by extension ALL drugs and treatments approved before 2000? And by even further extension, all research from any field that was not preregistered?

    If science was a factory, seeing this chart should make the foreman stop all conveyor belts because of production defects.

    • herculesorion says:

      Prior to Preregistration Of Primary Endpoints, the study method was “do a study, look at the data, find something that the data will support, pretend that thing was your primary endpoint all along and publish your study”

      After Preregistration, if you didn’t hit the original goal of the study then it was Null Result no matter what else you found.

      It’s not “everyone prior to Y2K was LYING”, despite what MoJo is telling you so that you’ll click on their website and look at the ads.

      Now, if you want to say “these studies may not have had enough data to confidently identify the effect they claim to have found, and if they’d been looking for that effect then they *would* have collected that much data” then you’re certainly right to say that. But this whole thing is being presented like some Freakonomics bullshit–“every science study ever done is WRONG!!!!”.

    • Douglas Knight says:

      Drug research is different from drug approval. Drug approval is based on research, but it is preregistered and the analysis is performed by the FDA. Also, it’s illegal for drug companies to show any other research to doctors.

    • brmic says:

      No, not at all. You should update in the direction that some past results were/are overly optimistic, and that standards have improved and are still improving.
      I think the study itself is mediocre and a bit sensationalist, and Kevin Drum’s treatment of it is awful.

      To list just a few criticisms:
      – The scatterplot suggests a triangle to me, consistent with lower hanging fruit being picked. But more importantly, I simply don’t see the discontinuity except in that there a few studies right around the cut point.
      – If you check sample sizes you’ll find that the pre-2000 results represent a total sample of 57k, with 22k of those coming from one study. The post-2000 sample size is 232k, so 4 times the pre-2000 sample size. This suggests a very simple explanation, namely that the pre-2000 results have a file drawer problem, coupled with the statistical necessity of anything significant in small samples being an overestimate. At any rate, the authors don’t discuss this.
      – However, they say they focussed on large scale trials with annual costs over $500,000, and that almost all of these are published, so file drawers are not an issue. Aaaah, yes. That’s were the list of sample sizes comes in again: Head to table S2, and find e.g. the FISH OIL study: 9 participants in both groups, and this supposedly cost over 500k? Let’s check the publication: https://academic.oup.com/ajcn/article-abstract/57/1/59/4715542 (there’s another fish oil study from the same year with different authors but similar sample size). Couple things come to mind: (1) if this cost over 500k/year, I’ll eat my hat. (2) This is not a ‘large scale trial’ by any measure. If this is really that expensive, expect lots of similar studies which went unpublished. (3) I don’t think the authors did a good job of selecting studies.
      – In line with that, note that the CAST study was excluded from the eye-catching graph. Mmmh. Does not raise confidence this is honest reporting.
      – While we’re at it, note that the eye catching graph is for primary endpoint AND that continuous primary endpoints are excluded AND that the authors note that mortality was reported in 24 of 30 trials pre-2000 (80%), which means two things: (1) they could very well have done the eye-catching graph for all-cause mortality with the added benefit of having a consistent outcome. Figure 1 with ‘primary endpoint’ is mixing outcomes like ‘death’ with ‘developed atrial fibrillation (y/n)’, which is a considerable limitation. That they don’t report Fig 1 for all cause mortality makes me suspicious. (2) That they want to sell the story of no-preregistration = outcome switching and thus try to downplay one outcome being consistently reported in almost all studies (Whether all cause mortality is being selectively underreported pre-2000 would require a look at the studies in question. If they’re like fish oil, then no, it’s perfectly benign that fish oil doens’t report mortality).
      – Ok, so what would the results for all-cause mortality look like? See Figure S2, meta-analytic overall null effects both before and after 2000 (The p-value in that line is for the heterogenity test, you need to check whether the CI’s of the overall effect include 1.) Do they mention that in their discussion? No, instead they treat it as gospel that there was a decrease around 2000 despite the fact that this is only true for one of their DVs (namely primary endpoint) and not true for the other. (At which point I’d like to acknowledge a commenter on PLOS One pointing out that this meta-analysis was apparently not preregistered and for myself wonder, whether there wasn’t a bit of outcome switching involved in the meta-analysis as well.)
      – On a content level, all these studies are ‘evaluating drugs or dietary supplements for the treatment or prevention of cardiovascular disease’. Yet when I look through the list of studies, directly acting oral anticoagulants (DOACs) are missing. This is certainly explicable in some way, but OTOH, DOACs are a major advance in the treatment of atrial fibrillation, CAD, MI etc., which I’d count as cardiovascular, and DOACs trials were published from around 2008 onwards. It’s a bit odd to not even mention that whole segment of studies, which might well have added some non-null results post 2000.
      – While on the subject of DOACs, it’s relevant to consider how those trials work: The aim is usually to show non-inferiority to warfarin (the standard drug) for a couple of outcomes and to show improvement over warfarin on some of those outcomes. Warfarin itself trades off bleeding versus thrombi, and so a better drug can lower either while keeping the other constant. Yet you only get one primary endpoint, and depending on which you pick the pre-registered trial is either null or not. The point is, in these kinds of things it’s often not clear, what the correct primary endpoint is and there’s a continuum from total pre-registration to measuring 30 outcomes and only reporting the best. In the middle you have studies which don’t much care a-priori whether they get fewer strokes or fewer myocardial infractions but they expect either or both to go down, and if it so happens that both decrease, yet one is significant and the other is not, then the significant gets written up in the paper in the spirit of putting one’s best foot forward. That’s ‘outcome switching’, but it’s outcome switching in the same sense as a meta-analysis highlighting a figure for one endpoint and not producing the figure for another endpoint.
      – In light of that, in turn, it looks to me like the data are most plausibly explained by some curious selection choices in the meta-analysis, more selective reporting and file drawering before 2000 and the low hanging fruit being picked as science advances.
      – For further conclusions about the relative importance of these factors, we’d need to see the analysis repeated: including continuous outcomes, including DOAC trials, lowering the financial requirement or raising it, preferably while addressing the sample size differences pre-2000 and post, and most importantly, doing this with something non-cardiovascular. Basically: We all believed, prior to reading the study, that forcing scientists to pre-register their studies keeps them honest and that file drawering and p-hacking are a thing we get less of with pre-registration. It would be very odd if the results said anything else and we’d be doubting the study design, not the theory, if they did. So, obvious things being obvious, what we really want to know is how strong the effect is. This study, in isolation, is a poor guide to that question, for reasons given above.

      • herculesorion says:

        If you check sample sizes you’ll find that the pre-2000 results represent a total sample of 57k, with 22k of those coming from one study. The post-2000 sample size is 232k, so 4 times the pre-2000 sample size. This suggests a very simple explanation, namely that the pre-2000 results have a file drawer problem, coupled with the statistical necessity of anything significant in small samples being an overestimate.

        I am amused by the irony of someone criticizing the statistical basis for the claims of a study claiming that studies generally lack statistical basis for their claims 😀

  10. Doug says:

    Thanks for this. Want to dig into the research when I get some free time later. But just want to say that very few people could do what you do, Scott.

    Admit a mea culpa, make a serious effort going through the research in an unbiased way, get yelled at by a bunch of people on the Internet, calmly and charitably pay attention to their points, double the effort to dig into the research, still remain unbiased and open-minded, without any other expectation other than getting yelled at by people on the Internet some more.

    I’ll probably do some yelling at you later. But for now, just want to say you don’t get a tenth of the appreciation that you deserve.

  11. Mr. Doolittle says:

    Pre-school and daycare programs seem to me to be aimed at two problems primarily, that have little to do with educational outcomes, that are not mentioned much, if at all, in the literature. They are sometimes discussed as add-on topics (and came up in the last post’s comments).

    1) Helping young and struggling families with childcare needs so that they can work, go to school, or otherwise advance themselves.

    2) Removing children from very bad environments in an attempt at providing positive examples that their home lives lack.

    I feel as though these are the actual reasons that we, as a society, push for Head Start and other pre-school programs. We also seem reluctant to talk plainly about these goals, with the exception of some quite recent Democrat pushes for daycare. The goalpost moving being complained about with the switch from “educational attainment” to “life outcomes” makes more sense if what we always cared about was closer to “life outcomes,” but wouldn’t have been accepted as a valid approach in the 60s. #1 is welfare wrapped in a different package (with associated baggage and complaints) while #2 is demeaning and would be incredibly insulting to talk about. What kind of disadvantaged mother would sign up for the “the state thinks I’m a horrible mother” program?

    This topic feels to me like everyone is kinda in on the real reasons, but we’re playing taboo and can’t talk about it in broad society. Anyone else get a similar impression?

    • Conrad Honcho says:

      The goalpost moving being complained about with the switch from “educational attainment” to “life outcomes” makes more sense if what we always cared about was closer to “life outcomes,” but wouldn’t have been accepted as a valid approach in the 60s.

      I think it’s more like people thought the purpose of school was education and educated people have better life outcomes, so improve the schooling. But after decades of believing intelligence / school performance was largely (half? all?) environmental, people are beginning to concede that no, significantly increasing intelligence is nigh-impossible and raising test scores is really really hard. I don’t think the initial advocates for Head Start deep-down knew this was the case and hid it. People thought early childhood education could make smarter adults, but no, not really, but it maybe can make better socially adapted adults.

      • Mr. Doolittle says:

        I agree that the original proponents would have made the connection from intelligence/school performance to environment as you say. On the other hand, if the goal was life outcomes, and education was a means, then they can drop education and not change direction. Even thinking that was the best method to achieve their goal did not tie them to that method.

        Bear in mind that Head Start was rolled out to the 300 poorest communities in the US, rather than a random sampling. Since very few 3-4 year-olds were receiving education at the time, if education was the only criteria, they could all benefit equally. It appears that the consensus was closer to my #2 above, in that case. With your addition, the implications of enrolling in the program would not be as harsh as I described, but I don’t see a way around the conclusion that the environment provided by those parents was…faulty(?) at best.

    • Douglas Knight says:

      I can think of a lot of other secret reasons people might have for promoting these programs. I think it’s a really bad idea to ally with people on the grounds that you’re all lying about what’s going on.

      • Mr. Doolittle says:

        I’m not thinking that there are intentional alliances here, at least not based on any known falsehoods. I think, as Conrad added, that there was a genuine belief that education was effective, and could be provided by this program. The goal of this education was improvement to “life outcomes.”

        What I’m wondering is if this specific program, of all potential programs, was actually selected for the two reasons that I mention. In that scenario, education is still valued and could be beneficial towards the ultimate goal of better life outcomes, but if the plan resulted in the improved results but education had nothing to do with it, that’s fine in the minds of the program’s supporters. I think there was a genuine hope that education was alone sufficient, but with a background thought along the lines of “Getting poor parents some day care and getting mistreated kids out of the home are also good, and worth running this program.” That additional line of thought is a lot harder to sell, so I would imagine it was not part of articulated reasons for the program. Hence a question – how much was the program designed around education, and how much around these other reasons?

  12. herculesorion says:

    The Terrible Awful Truth view: Maybe what “the effects are large but fade” shows is that most parents shouldn’t actually be parents, and the best thing to do for kids in low-resources(*) homes is to get them out of those homes. If you have the kids in high-resource environments (like a Head Start program) they do great; once they go back to “mom’s at work until nine, might as well just go on Instagram” they regress to the mean.

    (*) “low-resources” meaning a gestalt of income, cash on hand, assets, time, and family effort available to devote to child-care activities. I dislike saying “low-income” in discussions like this because income doesn’t always translate directly to assets; if you don’t make much money but you live in the paid-for family home that has enough room for grandma, then she can watch the kids.

    • Conrad Honcho says:

      If you have the kids in high-resource environments (like a Head Start program) they do great;

      That’s not what the studies Scott cited found. They found that the kids in Head Start might, do slightly better, in some areas of “life outcomes” and maybe worse in others but none of the studies consistently agree on which sub groups do better in which areas. Scott’s studies did not find that they do “great” or even “good.” Just maybe marginally not as bad. Maybe.

    • Mr. Doolittle says:

      I dislike saying “low-income” in discussions like this because income doesn’t always translate directly to assets; if you don’t make much money but you live in the paid-for family home that has enough room for grandma, then she can watch the kids.

      Just having a support network of extended family and friends can achieve that, even if you are renting or whatever.

      I agree with you that income doesn’t seem to, at least directly, determine the outcome. I don’t agree that “most” is the right qualifier for parents who shouldn’t be parents, but I don’t think we would find much headway on that question.

      • VivaLaPanda says:

        Totally agree, I think a more robust metric for home quality would be useful, outside just income. I grew up in a rural area where average incomes were really low, but lots of people owned the houses they lived in and were multigenerational.
        Hard part is that restricts your sample size…
        Ideally though, Income + Assets + Something to account for free childcare from grandparents/stay at home family

    • Statismagician says:

      This comes off as much more needlessly cruel than I think it’s meant to; ‘people without resources benefit from resources, this is not surprising and is not a strong supporting finding for Head Start as administered’ doesn’t benefit from being paired with what I can’t help but read as the implication that we ought to take children away from poor parents.

      If that’s intentional, I’ll just note that this almost certainly won’t accomplish what you want it to, and almost certainly will be horribly abusable and arbitrary.

      • herculesorion says:

        I’m not saying “get them out of the homes” as in “forced foster care”, but I’m saying that this evidence suggests that many people have more child than they can handle. The kids can sleep at home, but if they do great when they’re in Head Start and regress to the mean when they’re out, then the only reasonable conclusion is that whatever’s happening at home is not conducive to maintaining high cognitive performance and so they should be there as little as is feasible.

        • Mr. Doolittle says:

          They do well compared to children in similar demographics who do not go to Head Start. The regress to the mean happens during mandatory education (elementary school), when there is no control group of kids sitting at home anymore.

          Since kids without Head Start end up in about the same place as kids with Head Start by 3-4th grade, it’s difficult to draw the conclusion that you are. Not that it’s wrong, but that the evidence – purely in educational attainment – does not necessitate that reading.

          • herculesorion says:

            So, your argument is that the return to mean is not regression so much as the rest of the cohort catching up to them? That doesn’t seem to be borne out by the evidence.

            “Since kids without Head Start end up in about the same place as kids with Head Start by 3-4th grade, it’s difficult to draw the conclusion that you are. ”

            If the visibly positive benefits compared to cohort disappear when the treatment is removed, then the conclusion is not “the treatment does nothing”. If you want to say “the treatment benefits require reinforcement to maintain”, sure. If you want to say “the effect of cohort conformance is stronger than historical treatment”, also sure. If you want to put those together and say “you cannot expect long-term benefits from single early treatment followed by return to cohort without subsequent reinforcement, and if your goal is long-term effects then you need to find a different method”…sure, that’s definitely the case.

            But “PRESCHOOL DOESN’T WORK” is wrong.

          • baconbits9 says:

            If the visibly positive benefits compared to cohort disappear when the treatment is removed, then the conclusion is not “the treatment does nothing”.

            The question is what is the difference between 13 years of treatment and 14-15 years? If the answer is nothing then the extra 2 years did nothing.

          • Mr. Doolittle says:

            baconbits got it, but further

            But “PRESCHOOL DOESN’T WORK” is wrong.

            is uncertain. It may be wrong, but it may also be correct, especially depending on how you define the goals of preschool. If the goal of preschool is long term educational attainment, then “PRESCHOOL DOESN’T WORK” is correct. If the goal is long term outcome improvement, then we are at the maybe territory, as per Scott’s post.

            If the options were 1) Preschool + continuing education through 12th grade, or 2) no education, then preschool would clearly be the best option. If 3) K-12 turns out to have the same overall benefits as #1, then #1 is just adding expense for no reason. Let the kids go play!

    • vpaul says:

      The More Likely Mundane Truth view: parenting and shared environment have marginal effects as long as both are within reasonable boundaries. Have as many children as you want and will make you happy, it’s unlikely your work hours or home environment will make much of a difference and there’s nothing wrong with Instagram / TV / video games etc.

      • JohnBuridan says:

        The environmental choices accumulate into set of experiences and skills. I always bristle when people claim, say, that 6 hours of Fortnite a day is not harming their children. Well, it’s certainly not improving them. The benefits of Fortnite must be asymptotic. After 8 hours a week it seems like there are other fun and beneficial activities a child can do which will provide different benefits from Fortnite, hopping the neighbors’ fences to steal garden gnomes, playing board games and RPGs, reading an interesting book, volunteering, having conversations with adults, learning to meditate, visiting a library, playing various sports.

        There’s nothing wrong with Instagram provided your 13 year old daughter is not being emotionally scarred and abused by men in their 30s. Or TV, provided your kids are not being targeted with advertising to make them feel inadequate or unhappy. The tool which is not bad itself can be horribly bad for your kids. Parents should know the possible downsides of each tool.

        I reflected as a late teen on how much time my parents let me waste watching Nickelodeon. I thought it was a shame.

  13. Eponymous says:

    I think it’s reasonable to have a pretty strong prior towards a zero or tiny effect, both on general principles (i.e. Rossi’s iron law of evaluation) and given the evidence about lack of lasting effects from shared environment across many many studies.

    On the positive side, there’s the fact that giving free stuff to people should generally have *some* positive effect; and giving people free preschool (plus health screening and nutrition support) is definitely something.

    And really the evidence is pretty consistent with these priors. The things we don’t expect to (permanently) change didn’t really (permanently) change, and there maybe were some small positive results on other things.

    I’m a little concerned about selection effects in the sibling control studies (isn’t there a strong birth order effect?). But the RD design from the 1960s looks pretty good.

    In conclusion, I’ve revised somewhat towards there being a positive effect on some outcomes, though not academic achievement or IQ.

    I’m sure there are positive effects on the parents though, and short-term effects on the kids. Those matter in a cost-benefit analysis.

  14. Jeffery Mewtamer says:

    Some of my thoughts on this subject:

    Even if the benefits were large, immediate, and long lasting, I think the question of “how can we keep these benefits while lowering costs?” would be valid. That the benefits are small and either massively delayed or short-lived makes the subtly different question of “what aspects of the program are providing these benefits and whether costs can be reduced to a point the benefits justify them?” even more important.

    Though, given that the benefits are so delaid, I have to question the apparent lack of any acknowledgement of other interventions with more immediate results acting as additional confounders.

    I also agree that asking someone who has already studied the literature and summarized several important points in a manner that’s probably far more accessible than the literature itself if the literature covers a point of interest to the asker that wasn’t addressed in the summary as being a reasonable alternative to digging through the literature oneself. Gratned, I might be biased since even just following one of Scott’s links has a fairly high shance of taking me to a webpage that I have to fight with just to figure out how to get the content where my screen reader can read it with no guarantee I’ll actually understand the content. I can’t see any of the graphs Scott posts, but at least I know I’ll be able to understand what he has to say on the subject.

    Regarding things like race being proxies for less tagible things that vary with time, I do wonder how the results from these multi-decade datasets would compare with results derived from dividing the dataset by decade or year.

  15. Statismagician says:

    At an irresponsibly high level of abstraction, a high school diploma raises income by ~$9,600 (figures cited as from BLS) and Head Start costs ~$7,600 per child (Forbes, presumably citing the Federal DHHS), – just so we can get some figures to work with here.

    Manifestly, the program is not as incredibly effective as some particularly irresponsible defenders claim. Equally so, the educational component does not pay for itself. This is not necessarily the same thing as saying the program should be scrapped, and there is a large body of evidence supporting programs with similar* non-education aspects (see e.g. Parents as Teachers, Nurse-Family Partnership) effects on health and a similarly large pile of papers on small additions of parental resources (of which ‘time I don’t have to watch the toddler’ is pretty obviously one) having outsized effects on child and family outcomes. From Wikipedia citing CCR Analytics:

    90% of parents surveyed said that Head Start helped them to get or keep a job. 92% of parents surveyed said that Head Start helped them to enroll in an educational or training program. 99% of families surveyed said that Head Start helped them to improve their parenting skills, such as responding to children’s misbehavior and helping their children to learn.

    Plausibly, family benefits are more maintenance than improvement, and individual benefits come from parental education and medical interventions rather than educational ones and shouldn’t be expected to show up except in robust long-follow-up evaluations. Since these have been done on similar* programs with basically those results, and since dose-response is established in a couple of the papers Scott cites and the literature generally, if I were Secretary of Health and Human Services I’d try to economize on the preschool components as much as possible while expanding the home-visiting and medical aspects, but, c.f. Chesterton, absence of evidence of effectiveness is not evidence of absence of effectiveness. The full data are not in; presuming they will favor one side when they are is just as inappropriate regardless of which side**.

    Thanks, Scott, for providing a place I can point to whenever somebody asks me about this sort of thing (it’s happened before; occupational hazard). This is vastly better than my usual attempts to explain how weird social science research is.

    *Home visiting/early childhood education programs generally. Components include perinatal medical care and parenting skills instruction, as well as varying resources and ancillary services. These are usually more extensive than their equivalent Head Start interventions and therefore much easier to study.

    **This very explicitly does not apply to fixing the many and obvious problems with Head Start administration as currently done; nobody jump down my throat for supporting unrestricted government waste.

    • bizwacky says:

      I’ve got to push back on the math here. If I’m interpreting you correctly, you’re comparing a $7600 one-time program cost to a $9,600 average annual salary increase. If we could increase your income by $9600 a year from age 19 to age 65, that’d be worth about $235k in present value terms. Now admittedly, that happens 14 years after the expenditure for the program, so if we discount it by those years we’re down to a value of about $155k. The meta-analysis Scott mentions suggests that the head start programs improve kids’ odds of graduating by 11%. Assuming they’re targeting low-income schools, which have less than 60% graduation rates, we could ballpark the effect as being a 6.6% increase in graduations. That would mean a benefit in earnings of $10,270, which implies that the educational aspect of the program does in-fact pay for itself.

      Obviously there are major caveats here, one key I think is that these low-propensity to graduate students likely don’t see those huge earnings jumps, and that factor is one thing you’d want to directly study. However, there may be areas other than incomes that head-start improves, i.e. likelihood of criminality, that also yield significant societal benefits. It’s not clear at all to me that the program would fail a cost-benefit test, given the information we have today.

      • Statismagician says:

        Sorry, I used the ~5% graduation rate improvement figure from one of the studies, not the meta-analysis, and somehow didn’t think to specify low-income schools. Another illustration of why showing your work is important, I guess – thanks for checking.

        Agree entirely with your second paragraph.

        • bizwacky says:

          Yeah, this is all obviously very sensitive to our assumptions, with the reasonable assumption of a 5% improvement it doesn’t look nearly as good. I think the point I was going for was that, contrary to some other commenter’s assumptions (not yourself), Head Start could very plausibly be a good use of taxpayer money. Now there’s certainly a lot of uncertainty (or is it uncertainly a lot of certainty?), but that still puts it well ahead of probably 90% of federal programs that we could be looking at.

  16. Garrett says:

    Other question to consider based on some of your statements:
    How much of this is possibly due to having a person with a large amount of experience with young children telling the parents “there’s something not-right with your kids and you should see a pediatrician” and thus getting children (hopefully those with correctable medical problems) into the healthcare system sooner? It could be that poorer/single/more-encumbered parents would be less-likely to take their kids in for well-baby visits. This is somewhat reflected in the anemia study that you mentioned above. But it could also be reflected in earlier detection of needing glasses, learning disabilities, avoiding vaccinatable diseases, or other medical conditions.
    If so:
    1) Could this be addressed instead by sending around a home health nurse to perform check-ups on children at-risk?
    2) Would passage of things like CHIP result in similar findings?
    3) Would the ACA’s mandatory coverage of well-baby visits have addressed the same issue?

    • Statismagician says:

      1) – Yes, and is in lots of better-studied programs (Nurses for Newborns, Nurse-Family Partnership, [Nurse + [select any family word] [select any relationship word] ad infinitum] which show significant positive effects.

      2) and 3) – As these programs were intended, probably. As implemented, probably not; any program based around health insurance misses a lot of people who would really benefit from the program, because [America].

  17. arlie says:

    I’m somewhat amazed/apalled at all the emphasis on racialized sub-groupings in these studies, or perhaps in your writeup, and finding it easy to think up all kinds of confounders. Suppose we assume that there is no systematic difference among racial outcomes here, but there is some other difference, which I’ll call X. X does not consistently correlate with race – in particular, the different studies have different proportions of X in their racial subgroups. E.g. one study has it more common in their blacks, and another has it more common in their whites. (Of course there’s no attempt to match racial subgroups across the studies.) That, plus small samples/low statistical significance seems to account for all these rather bizarre differences.

    Looking for X makes sense – maybe it’s something we can affect (e.g. having your preschool teacher the same/different race as you) – or maybe it’s something that can let us pick the best candidates for scarce preschool funding. But all this nattering about race? It seems to be kind of insignificant.

    But then, contrary to received opinion, I don’t think that e.g. individual blacks are more similar to each other than they are to particular individual whites. And it’s bizarre to see e.g. urban/rural differences not even mentioned.

    • The Nybbler says:

      And it’s bizarre to see e.g. urban/rural differences not even mentioned.

      For the study with the 300 poorest counties in 1965, I’d be surprised if any of them were urban.

    • Scott Alexander says:

      I didn’t have time to look into this enough, but these studies often differed in which of the races analyzed was poorer. Sometimes blacks were poorer because this is the standard US average. Other times whites were poorer – I think because as part of attempts to fight racial inequality Head Start was targeted more towards blacks, so a broad cross-section of blacks but only the poorest and most disadvantaged whites were involved. If I were looking into this more, I would check how this affected results.

    • Randy M says:

      I’m somewhat amazed/apalled at all the emphasis on racialized sub-groupings in these studies

      I believe this comes from trying to find some subgroup with a significant effect when it isn’t present for the whole group.
      The other factor is that we have a racial education gap in America, and everyone really wishes we didn’t, so if it is possible to change that in any given intervention, it’s going to be called out or checked for.

  18. vpaul says:

    Did I miss where you dealt with the Tennessee Prekindergarten Program Study? (significant negative effects): https://www.sciencedirect.com/science/article/pii/S0885200618300279

    I would be willing to bet that a high quality study will find no effects (not counting a subgroup analysis), for pre-k programs implemented in the real world (without an additional medical screening / intervention component).

    I am concerned about researcher degrees of freedom and bias with these studies. And the strongest study imo, the regression discontinuity study by Ludwig and Miller, could be explained by the affects of improving anemia or other health related interventions. Though that study and the Norway study seem strongest. I am skeptical of the sibling control methodology.

    • Scott Alexander says:

      My impression is that Tennessee only looked at early childhood test scores, which I’m admitting there’s no effect on.

    • Statismagician says:

      The National Institute for Early Education Research says the Tennesse Prekindergarten Program was particularly bad. during the study period, and has since been modified. The study authors mention the same data, but say it’s not indicative of an unusually bad program; I don’t know enough about the metrics to comment on who’s right, but if it’s NIEER then that explains things quite neatly.

  19. Deiseach says:

    a positive and implausibly large effect of Head Start on the probability that a white mother was a teen at the first birth” which they say is probably sampling error

    Well, no? If the Head Start programme is aimed at the disadvantaged (which seems to be another way of saying “the poor”), then what grouping is most likely to have a large cohort of single teenaged first-time mothers? Think, think… can anybody solve this conundrum? For instance, the Guttmacher Institute website has a section on “which US states have laws permitting minors to consent to pre-natal care” where they seem to define minor as “17 or younger” (while noting that some states have specific ages like 12 or 14. I hope this is an artefact of old ‘age of consent/marriage’ laws, and not “our state has so many 12 year olds getting pregnant we needed to include this in the law”).

    Let’s get some more helpful information here:

    Unintended pregnancy rates are highest among poor and low-income women, women aged 18–24, cohabiting women and minority women. Rates tend to be lowest among higher-income women, white women, college graduates and married women. For example, in 2011, the rate of unintended pregnancy among higher-income white women was less than half the national rate (18 vs. 45 unintended pregnancies per 1,000 women aged 15–44).

    Traditional estimates understate the risk of teen pregnancy among adolescents because they typically include all women, whether or not they are sexually active. When rates are recalculated including only those sexually active, women aged 15–19 have the highest unintended pregnancy rate of any age-group.

    Who is eligible for Head Start?

    Eligibility is largely income-based, although each local program includes other eligibility criteria, such as disabilities and services needed by other family members. Families must earn less than 100% of the federal poverty level. Families may also qualify under a categorical eligibility category—receipt of Temporary Assistance to Needy Families (TANF) funds, Supplemental Security funds, or Homeless, as per the McKinney-Vento Act. Up to 10% of any funded program’s enrollment can be from higher income families or families experiencing emergency situations. All programs are required to provide services to children with disabilities, who must comprise 10% of their total enrollment. Per the Head Start Act (2007), programs may elect to serve families whose income is between 100-130% under certain circumstances. Programs must also complete additional reporting requirements if this is appropriate for their community.

    Yes, to this ignorant person, “large effect that a white mother was a teenager at the first birth” overlapping with “Head Start is a programme targetting the disadvantaged” looks like what you’d expect, not some weird freaky sampling error.

    EDIT: The CDC has a nifty graph about “birth rates (live births) per 1,000 females aged 15–19 years for all races and Hispanic ethnicity in the United States, 2007–2015”.

    White (non-Hispanic)
    2007, 27.2
    2011, 21.7
    2012, 20.5
    2013, 18.6
    2014, 17.3
    2015, 16

    White women do have the lowest rates of all the ethnicities listed, but the CDC also has a helpful breakdown on “Socioeconomic disparities”:

    Socioeconomic conditions in communities and families may contribute to high teen birth rates. Examples of these factors include the following:

    – Low education and low income levels of a teen’s family.
    – Few opportunities in a teen’s community for positive youth involvement.
    – Neighborhood racial segregation.
    – Neighborhood physical disorder (e.g., graffiti, abandoned vehicles, litter, alcohol containers, cigarette butts, glass on the ground).
    – Neighborhood-level income inequality.
    – Teens in child welfare systems are at increased risk of teen pregnancy and birth than other groups. For example, young women living in foster care are more than twice as likely to become pregnant than those not in foster care.

    So yeah, I’m going to stick my neck out and say that for poorer white women with child/children enrolled in a Head Start programme, teenage single motherhood isn’t that anomalous a result.

  20. Douglas Knight says:

    There’s an innocent explanation here, which is that everyone was very close to the significance threshold, so these are just picking up noise. This might make more sense graphically:

    It’s easy to see here that both studies found basically the same thing, minus a little noise, but that Study 1 has to report its results as “significant for blacks but not whites” and Study 2 has to report the opposite. Is this what’s going on?

    I know that you went on to check and see that this isn’t what was going on, but this can’t possibly be what’s going on. If the two groups had effects close to significance, the pooled group would be definitely significant, because the larger sample size means smaller sampling error, able to detect smaller effects.

  21. Deiseach says:

    Following on from the above, I know anecdotes are not data, but I’d like to throw some opinions into the ring here.

    For whatever reason, I seem to have moved on a career trajectory involving clerical work/administrative support work from adult and continuing education (including adult literacy centre and various training/educational/re-skilling schemes for the unemployed, those returning to education, and those looking to change jobs), to a secondary school (ages 12-18 years) in a designated DEIS (Delivering Equality of Opportunity in Schools, the Action Plan for Educational Inclusion which focuses on addressing and prioritising the educational needs of children and young people from disadvantaged communities, from pre-school through second-level education (3 to 18 years) area (varying from “Disadvantaged” to “Very Disadvantaged” educationally) and including the service for early school leavers, to social housing, to where I am now in services for children with additional needs (ages 2-5 years).

    It’s surprising/disheartening how I’ve seen many of our “clients” moving right along that trajectory (and then when falling through the cracks, reading names I recognise in the court pages of the local papers) from “kids from disadvantaged homes” to “single parents themselves of kids from disadvantaged homes”.

    So from my uninformed and purely subjective viewpoint, what are all these educational disadvantage programmes about?

    They’re not about “start little Johnny/Jamal/Lupita on free pre-school and they’ll have high grades, graduate high school, go on to college, and get a Good Job with that degree so they become productive, contributing citizens and aspirant members of the middle-class!” Sure, you have to sell them to the public (who are the taxpayers funding these programmes in the first place) like that, and the idealists in education and government probably start out believing that, but in reality they are not going to turn little Johnny from the block (with very few exceptions) into a guy graduating with an MBA from Harvard. So what are they about?

    Until you’ve worked with/seen the disadvantaged, you don’t really have any idea what their lives are like. Scott saw some of that with his patients in the Midwest, but those were adults. Here we’re talking about the other end, kids.

    Some parents/caregivers are trying their damn best but are stuck in bad situations. Some parents/caregivers are trying their damn best but can’t do much because they’re hampered themselves (literacy difficulties, unstable lives and upbringing themselves, lack of education, and so on). Some parents/caregivers are goddamn stone-cold psychopaths and as fucked up as the care system is, it is better than leaving the kids with them (if the social workers were any damn use, they’d yank the kids out of those homes).

    (For that last, I have one particular example in mind but it’d probably be slanderous/libelous/fifty other things that would bring the law down on here if I said anymore).

    So what intervention programmes and educational disadvantage programmes and all the rest of it try to do is get the kids into some form of schooling and keep them there as long as possible. The schools are not expecting to turn out a crop of “will get into Top Ten colleges” students, they know their place on the pecking order and that the kids who are going to go to those colleges are not attending this school. But what is the alternative? The kids drop out at fifteen (or younger), they’re hanging around home or more likely on the streets, they’re going to get into drugs, the boys will probably end up on a petty crime lifestyle to jail, the girls will probably end up getting pregnant as single teenage mothers, and the whole cycle repeats itself all over again.

    Head Start and free kindergarten and all the rest of it is not about turning disadvantaged kids into baby geniuses. It’s about supporting the families who are making some kind of effort and mitigating the damage of the families who don’t give a fuck about their kids as anything more than tokens to extract goodies for the parents from state bodies, charities, and do-gooders. It is about socialisation because in some cases the kids are damn near feral. It is about introducing structure into their lives, teaching them basic concepts of being a human, and if you’re lucky, getting some education on top of that. And hopefully, helping the families to keep them in education as long as they’re able so they have some option other than “take a minimum wage unskilled part-time job or go on the dole”.

    • jasmith79 says:

      if the social workers were any damn use, they’d yank the kids out of those homes

      Contrary to popular belief, social workers do not remove kids from homes. Courts do. Any social worker who deals with at-risk children can regale you with terrifying tales of kids in homes that no one in there right mind would leave a child in smashing up against the brick wall of judge who doesn’t meet that bar.

      Nor is it as simple as your describing. Many parents will clandestinely attempt to contact their children, and the children often facilitate the process because, well, it’s their parents. Meaning that even in the best case scenario where the courts agree it might not have much impact.

      Social workers are people. Some are better people, some worse. Some are better at their job, some not as much. Don’t let frustration at a negative equilibrium cause you to lash out at people trying to the best of their abilities to mitigate it.

    • nameless1 says:

      And yet the cycle will most likely repeat itself. It will, as long as we don’t decide that helping requires some tough choices, that there is a difference between compassion and sentimentality and long-term fixing the cycle requires some unpalatable moves. I think I would give a mandatory contraceptive implant to every teenager and there would be some basic conditions to having children and thus having it removed, and instead of welfare if the parents cannot provide a suitable environment for raising kids out of their normal income, they would be taken away. Harsh and Orwellian and all that, but at least every step of this would prevent much and cause little suffering, and either this or just go darwinian libertarian and let everybody – and their innocent kids – face the consequences of their choices. But the idea of personal freedom combined with a helping social system, so the combination of personal freedom allowed and yet the consequences of it mitigated just leads to the proliferation of bad choices. The gentle and humane thing is, however Orwellian it seems, is to not allow some of the worst choices. A line has to be drawn somewhere. And the line is pretty clear to me: everybody is allowed to screw up their own lives, but not of their kids or future kids. Hence don’t people become parents unless properly ready for it and take the kids if they stop being able to be good parents, which includes enough income. I don’t see any other solution than to draw the limits of personal liberty between people and their kids.

      • eyeballfrog says:

        if the parents cannot provide a suitable environment for raising kids out of their normal income, they would be taken away

        cause little suffering,

        OK then. I take it you have never had kids, nor been particularly close to any children in your life.

        Anyways, standard objections apply: Who gets to draw the line? How likely is widespread compliance with this system? How disastrous is the failure mode of this system getting captured by bad actors?

    • Plumber says:

      @Deiseach

      “…., I know anecdotes are not data, but I’d like to throw some opinions into the ring here…”

      Those anecdotes seem very much like data to me Deiseach.

      Far too many have just been “dealt a bad hand”.

  22. danculley says:

    These are interesting and I have to admit I never would have researched to this degree on my own, so thanks much for that. All that said, none of the studies really describes a mechanism of action for the delayed effects with falsifiable predictions that would differentiate it from other causes. Of course none of them purport to really be anything other than exploratory, so that’s not a criticism of them so much as of how they are interpreted. But given all the noise and confounding subgroup effects, an actual theoretical model is desperately needed…

  23. divalent says:

    A random thought: besides whatever academic activities and skills Head Start aims to develop (and which the data suggest has no lasting effect), the environment also exposes these children to our cultural and social norms, values, and expectations at a younger age than kindergarten. And probably also exposes them the a somewhat larger subset of society than they would have experienced at home. (And a head start on developing social connections with a larger pool of others.) What is the difference between a kid who drops out of high school and one that completes it, if academically they were the same? It’s certainly not the satisfaction they get from whatever they achieved in the classroom, because the data says that wasn’t different. It seems reasonable to guess that it was something the graduate valued that the drop out did not. Why is a Head Start kid more likely to stick it out? (Is it significant that the one subgroup (in one study) where Head Start appeared to have the biggest impact on HS graduation was with hispanic kids?)

  24. DNM says:

    I can maybe be convinced that this is enough evidence to continue funding preschool.

    I am not convinced there is anywhere near enough evidence to make it mandatory. As you state, “Going deeper into these results supports (though weakly and informally) a model where, when daycare is higher-quality than parental care, child outcomes improve; when daycare is lower-quality than parental care, child outcomes decline.” So why is that the direction of the trend?

  25. j r says:

    I tend to agree with the bottom line that the evidence does suggest that preschool has some positive life outcome effects that cannot be explained away. But I’m still not quite sure how “wrong” your previous position was. Maybe that’s because I presently hold both of these positions and I don’t really see a conflict. That is, there is no conflict between the belief that preschool has some demonstrable positive effects for certain kids and the belief that the mainstream position on preschool is absurd and divorced from the reality of the evidence.

    For instance, here is an article from the NY Times Magazine that pretty well sums up the mainstream position: https://www.nytimes.com/2018/01/09/magazine/why-are-our-most-important-teachers-paid-the-least.html. The title alone says it all. And even once you get past all the selective siting of the literature, there’s the fact that the argument about education comes bundled with all sorts of other generically progressive positions that have nothing to do with education. For instance, that claim that the reason that we don’t pay preschool teachers enough is that we undervalue women’s work. I don’t know how to describe this position as anything other than unserious. And yet, this is the the NY Times Magazine.

    And here is the relevant bit from the Democratic Party platform:

    Democrats believe we must have the best-educated population and workforce in the world. That means making early childhood education and universal preschool a priority, especially in light of new research showing how much early learning can impact life-long success. Democrats will invest in early childhood programs like Early Head Start and provide every family in America with access to high-quality childcare and high-quality preschool programs. We support efforts to raise wages for childcare workers, and to ensure that early childhood educators are experienced and high-quality.

    In both of these examples, what I see is a kind of shell game being played between the three propositions below:

    1. there is a “high quality” preschool experience that probably can raise academic achievement and positively impact life outcomes
    2. there is a “good enough” preschool experience that is basically daycare, which has no discernible impact on academic achievement but does positively impact life outcomes for some children
    3. there is a “no preschool” experience, which is probably detrimental to kids coming from poorer, more dysfunctional backgrounds but has not much of an impact on kids from wealthy, educated parents

    The promise of the “high quality” experience is held out, without bothering to mention that it basically impossible to scale and replicate. The possibility of no preschool is portrayed as deprivation without bothering to mention the qualifiers. And the “good enough” option is a characterized as a failure to heed to research, when in fact it’s probably the option that best fits the research.

    • JohnBuridan says:

      Helpful analysis!
      I am thinking about what a good piece of legislation would be at the State level to secure the “good enough” option for the most poor townships. Perhaps something like:

      Shall the State impose a 0.05% increase in taxation in each tax bracket in order to fund early childhood education in the poorest townships of the State. Townships which vote that they would like to participate in the program and who have a per capita income of under $16,000 are eligible for the program.

      @ j r What do you make of this Jacobin article? https://jacobinmag.com/2018/08/a-blueprint-for-universal-childhood
      I’ve been looking for an interlocutor to discuss it with.

  26. nadbor says:

    It’s funny how everyone is focusing solely on far-off adult outcomes and the child’s present well-being does not even enter into consideration on its own merit. It’s as we silently agreed on some perverted version of utilitarianism where the total value of a life proportional only to the the contribution you make to the nation’s GDP.

    I don’t watch a Disney movie with my daughter to raise her expected lifetime earnings in some circuitous way. I do it because we both enjoy it. Is that not good enough?

    Isn’t it weird that the question of whether the children are happy in preschool not on the list of questions considered when we decide whether to send more children to preschool? (ditto for the happiness of the parents!)

    • stationarywaves says:

      Good comment and very important point.

    • Mr. Doolittle says:

      This is the kind of thing that connects with my question above. For a program explicitly about the wellbeing of children, we don’t seem to be paying much attention to the children. The lends credence to the idea that the program is instead about the parents of those children – whether a benefit to them or a punishment for being bad parents.

    • M says:

      Unfortunately that sort of thing is not measurable, while GDP (even with all the controversy about what it means) is.

      It is also not deliverable by Head Start, or any other functioning or proposed early years initiative that I know of. I’m not even sure how you would design it.

    • baconbits9 says:

      I’m going to go out on a limb and assume that your daughter doesn’t watch movies 6 hours a day, or that you don’t feed here cake and ice cream 3 meals a day, and that most of your daily activities aren’t about making her happy right then and there in the moment.

      Individual happiness is a terrible metric to go by, we can’t measure it well, its highly relative meaning we can make other activities lower in happiness by shoving high happiness events down our kids throats and short term enjoyment doesn’t correlate well with long term satisfaction in life.

      • stationarywaves says:

        Why do you suppose that nadbor had only short-term happiness in mind?

      • nadbor says:

        We go to the park, play a video game, watch a movie, go bouldering or swimming together, have a picnic with my friends or a playdate with hers. It’s a compromise between our (the parents) and their (2 daughters) short and middle-term happiness under the constraint that long term physical and mental health is not too damaged. So we’re not doing cocaine and only eating reasonable amounts of ice cream and cake.

        Anyway. I never said that I would do the studies differently. I only said that it’s weird. And it is weird to do some intervention ostensibly to make the little Johnny better off and then measure everything and the kitchen sink except whether it makes him better off. Why measure education which is a predictor of earnings which are a proxy for utility while completely disregarding utility itself?!

        But of course I know why. I can think of lots of reasons why government programs don’t directly optimise for happiness, some of them good. I just find it ironic.

    • cassander says:

      You watching a disney movie with your kid doesn’t cost me and the other tax payers $7,600.

  27. stationarywaves says:

    It seems as though we’re putting a lot of emphasis on the impact of Head Start. What if the effects of Head Start don’t generalize to other forms of preschool? Especially considering that the government was involved in establishing and promoting Head Start, possibly to the disadvantage of competing models. And how does Head Start fare in a head-to-head comparison of any other preschool system?

    But there’s a more important point to be made here. Any time I see statistical results so close to the significance threshold, and yet going so many different ways for so many different segments in so many different studies, I start to wonder if the regression model is really doing the work we think it is.

    To wit, maybe preschool has a widely varying impact on individual children; some kids love it and thrive within that environment, some kids hate it and never should have been there. Maybe there is no way to look at race and income, and then predict how preschool is going to impact their lives. Maybe human individuals are susceptible to human individuation and thus we cannot ever conclude that “PRESCHOOL IS GOOD” or “PRESCHOOL IS BAD.” Maybe the best we can ever say is, “Preschool worked for Johnny, but Bobby would be better off spending more time at home.”

    And maybe that’s okay. Maybe it’s okay that no one thing has roughly uniform impacts on an entire human population. Maybe it’s okay that we take these things on a case-by-case, child-by-child basis.

    • cassander says:

      I don’t think anyone has claimed that pre-school is actively harmful. the lines drawn in this battle are between “pre-school is so good we should spend tens of billions of dollars on it.” and “I’d rather not.”

      • stationarywaves says:

        That’s probably true, and consistent with my over-arching point that perhaps this is not a decision that statistical analysis can support. It may be a decision best made at the individual level.

        I suppose that if by “we” you mean “the government,” that places me in the “I’d rather not” camp, but for me this has more to do with epistemology than p-stats.

  28. Charles Littlewood says:

    Being a bad person, I think that people shouldn’t have children if they can’t (or at least won’t) take decent care of their children. I think we should try to find ways to reduce the number of children such people have. Maybe pay them to get sterilized or at least use Norplant.

  29. Charles Littlewood says:

    A much more effective way to have American children turn out better is to start with better raw material.

    Grandchildren of Low-Skill Immigrants Have Lagging Education and Earnings

    https://www.cis.org/Report/Grandchildren-LowSkill-Immigrants-Have-Lagging-Education-and-Earnings?utm_source=E-mail+Updates&utm_campaign=b6609d1ea9-EMAIL_CAMPAIGN_2018_11_14_01_00&utm_medium=email&utm_term=0_7dc4c5d977-b6609d1ea9-44723357

    • Despite the title, this is specifically about Mexican immigrants. It does not, for instance, include me, although I am a grandchild of low-skill immigrants.

      And the figures show the descendants of immigrants doing better generation by generation, although average wages and college graduation rates are not yet up to those of the white population.

      • Charles Littlewood says:

        “And the figures show the descendants of immigrants doing better generation by generation, although average wages and college graduation rates are not yet up to those of the white population.”

        Maybe these average wages and college graduation rates will eventually converge to those of the white population (and maybe not) but don’t you think it makes sense to put a lot of importance on the next generation or two?

        I think in Economics there’s this concept of “Discounting the Future”. Maybe you’ve heard of it. To me at least, what happens next year is a lot more important that what happens a million years from now.

  30. regularjoeski says:

    This study probably explains all the improvement. https://www.nber.org/papers/w25254#fromrss
    It states that having the same race teacher once gives you the same results as seen in the Pre-K results. None of the studies you quote thought to report this covariate. I leave the implications to the reader.

    • sscJohnSmith says:

      > It states that having the same race teacher once gives you the same results as seen in the Pre-K results.

      Not quite, it says that for black students having a black teacher helps. No obvious reason for that covariate to actually vary in a systematic fashion occurs to me. My first thought is that the result can be explained by black teachers beign better at getting black students to behave.

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