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Comment by po | Hacker News Reader

I feel like you maybe should shop around for a new pet peeve. Wasn't the data on this pretty clear due to various countries, states, cities banning lead at different times? My understanding is that you can see a corresponding drop in lead levels in the blood, rise in IQ, and reduction in crime 20 years later.

https://en.wikipedia.org/wiki/Lead–crime_hypothesis#Correlat...

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Tying lead levels to crime levels seems super sketchy to me when there are plenty of other factors that get studied and seem to have much better correlation and even causative effects. Hell, violent crime has started creeping back up in recent years, but to my knowledge the lead levels are not.

Violent crime "creeping up" is entirely dependant on whose reports and which methodology relative when it changed .. see (for example):

https://www.themarshallproject.org/2023/11/03/violent-crime-...

Whichever way that data is cut, though, pre-2000 and in particular mid 70s "peak lead" crime levels are far and away worse than those of the past two decades.

That's fine, but I don't think there any causation in that correlation. I've never heard a compelling argument to explain it when there are tons of other compelling factors (organized crime, economics, opportunity, surveillance technology, testosterone levels, even birth control and abortion).

Edit: why disagree? I can claim that the size of the standard Hersey bar had a positive correlation over that time too. That doesn't mean there's a convincing causative mechanism. Most of the studies linking lead to crime rely on poor data practices, such as testing blood levels of convicted criminals. There are very easy explainations to show bias here, such as smarter criminals being less likely to be convinced and criminals with higher blood levels tending to have lower IQs. Many exclude certain areas like DC or NYC in their analysis or the trend disappeared. Many used state level data points which are not granular enough to investigate causative effect (eg median income at the state level is not useful. You need to investigate it at the individual level. Things like localized cost of living and standard of living would also be more useful numbers). The designs and data are sloppy as hell in my opinion.

Yeah that's not how it works though... nobody is saying lead causes violent crime. Nobody is claiming crime can't go back up without lead. Of course there are better causative factors.

It's just that meta-analysis over many studies seems to show that it is a contributor to crime. When it is removed from the environment, it then shows up in the crime data.

"nobody is saying lead causes violent crime...

many studies seems to show that it is a contributor to crime."

This seems contradictory. How can it not cause violent crime yet be a causative factor?

I can see how it might be correlated. But I've never heard a compelling argument for how it would be causative.on any significant level.

Sorry, When I said "nobody is saying lead causes violent crime" I meant "nobody is saying lead is the sole cause of violent crime."

Please do share if you're aware of any sources associating population-wide lead level decreases to population-wide IQ increases. While we can't be certain about blood lead levels before the mid-20th century, my impression is that the golden age of the Flynn effect (mid-20th century through the mid-70s) was concomitant with explosive growth in the use of leaded gasoline, which should be far and away the primary driver of elevated lead levels, and that cognitive scores have been relatively flat from the mid-70s onward as lead levels have decreased precipitously.

Edit: It's worth noting that the study described by the OP does not demonstrate an effect on IQ. They estimate population-wide lead exposure. The lost IQ point calculation is based on correlation coefficients obtained through observational studies.

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