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Comment by jeffbee | Hacker News Reader

So, the evidence for this hypothesis is extremely strong. There have been studies of children who did or did not get treated for high blood lead levels, and those who did not had much higher rates of criminal behavior. These were children from the same schools, same neighborhoods, same time. All the confounding circumstances are controlled.

The Lead-Crime Hypothesis may also refer to the idea that lead is the main reason for the global crime wave that peaked in 1990. The evidence for this is less convincing.

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The strong evidences you are talking about are usually confounded by socioeconomic status. One recent longitudinal study in New Zealand have found only a very weak correlation:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5801257/

That study isn't as powerful as what I mentioned. That is a longitudinal study of children who were exposed to lead, and their life outcomes. The study I want to mention was of children, all of whom were exposed to lead, but only some of whom were treated for it, based on a threshold of blood lead concentration. Figure 4 in this paper is particularly compelling. They show a strong correlation between blood lead levels and violent criminal behavior in later life, but the intervention group, who were exposed to lead but received treatments for it, had much lower rates of crime.

You should read it to see if you think they didn't control for socioeconomic factors well enough. Section II and Table 1 in particular. https://pubs.aeaweb.org/doi/pdfplus/10.1257/app.20160056

If one were receiving treatment for lead, wouldn’t that correlate with socioeconomic status? I’m sure many poor people went untreated and poverty leads to violent crime. Which page addresses this? I’m too lay to understand.

The treatments in question are administered by the state, at no charge, and some of them are mandatory.

It's really not a long paper. Go read it.

In the U.S., yes. In the rest of the developed world, no.

Impoverished children and expecting mothers have access to medicine paid by the government/taxpayer in the US through Medicaid

I know it's fun to posture about how backwards the US healthcare system is but we actually do literally have the system in place that you're virtue signaling about us not having, as it applies to children

People act like the US has no welfare at all and it just isn't true. Children whose parents can't afford treatment can still get treatment, and have been able to for more than half a century.

My own niece was born in a hospital because of this. My adult sister received treatment for her collapsed lung at the same time, paid for by the taxpayer, because she couldn't afford it.

Medicare and Medicaid might not be perfect but acting like the US has no safety net is a lie

In an shorthand comment, I’m not sure if we can differentiate if the commenter was saying there is literally no safety net, or if the safety net is insufficient, and arguably unevenly applied based on region and race. One anecdote of someone reviving a medical service is certainly not sufficient for a discussion of the latter.

Whenever a treatment is given based on a strict income threshold you have a nice natural experiment. Those who have income <= T receive treatment. Those who are > T (even one dollar above) do not. Therefore, those who are "near" T are a great cohort to study effects of the treatment, since their socioeconomic factors are so close.

It sounds like the parent comment was saying exactly this occurred for children exposed to lead, and those in the treatment group went on to have better outcomes.

EDIT: Looking through the abstract, it appears the threshold was on blood / lead concentrations. This means those who differed only a tiny amount in lead concentrations received different treatments (some vs none), and had different outcomes despite being similar in all other metrics. Figure 4 was pretty interesting.

No, the treatments were all paid for by the government of North Carolina in this case, and were based on levels of lead concentration in the blood, not socioeconomic status. So by comparing those with slightly above the threshold (who got treatment and thus ended up with significantly lower lead levels in their blood) and those with slightly below the threshold (who did not receive treatment and therefore ended up with higher levels of lead in their blood) you can make an estimate of the effect of lead in the blood that should cut across SES. (This is described on page 316 of the pdf- actually page 2- if you tested above the 10 microgram/deciliter concentration twice you got treatment, if you tested above only once you did not get treatment. They did a matched control group where the initial tests matched a test in the treatment group and generally matched the SES and geography, but the second test was in the 5-10 mcg/dcl range. Thus there is strong evidence that the control kid had a blood-lead problem but just missed the cut-off for government treatment.)

> All the confounding circumstances are controlled.

How can you control everything? These studies do not control what no one thought about that it could have an effect. Its impossible to control everything.

It's as close as you'll get to a random controlled experiment on this topic, because an actual controlled experiment would not be ethical. Studying people from the same school who lived in the same neighborhood at the same time controls a hell of a lot of the usual confounders.

True. Perhaps one possible confounder though is that parents who are attentive enough to think about lead paint and test for it / paint over it / remove it are also more clued in on other matters.

One of the studies I'm thinking of relies on the boundary effect, where children who tested with 100µg/dl of lead in their blood were all treated and those with 99.99µg/dl were not, and this threshold (I'm not sure exactly what it was) is way too high.

Right. The same issue confounds studies that show charter schools perform better than their public school counterparts, after controlling for student demographics. It could be that the quality of a charter school education is truly better, but it’s also possible that parents who care enough about their kids’ education to take initiative to send them to a charter school provide a better home environment in general.

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