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I just found an article titled "America's Real Criminal Element: Lead" via Hacker News that made an assertion about the cause of violent crimes that I found rather surprising.

The article states that the addition and later removal of lead in gasoline is responsible for a large part of the rise and decline of violent crime:

Put all this together and you have an astonishing body of evidence. We now have studies at the international level, the national level, the state level, the city level, and even the individual level. Groups of children have been followed from the womb to adulthood, and higher childhood blood lead levels are consistently associated with higher adult arrest rates for violent crimes. All of these studies tell the same story: Gasoline lead is responsible for a good share of the rise and fall of violent crime over the past half century.

On first glance, most of the cited data seems to be about finding a correlation between lead and violent crime, the causative link seems to be much weaker. While it might be plausible that lead poisoning has some effect on later violent behaviour, I find it hard to believe that a major part of the increased crime between 1960 and 1990 was caused by lead.

Is there strong evidence, preferably not only correlations, that show that lead poisoning is responsible for a large part of the rise and fall of violent crime in the United States?

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    Phrases like "Fill them full of lead", common in old gangster movies, suggest causality in the other direction: that the rise of violent crime leads to a higher incidence of lead exposure.
    – Paul
    Jan 4, 2013 at 17:54
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    What do you mean when you ask for more than correlations? Do you want controlled experiements that put lead into children to see whether it makes them violent as teenagers? What kind of ethic board is supposed to sign on such an experiment?
    – Christian
    Jan 4, 2013 at 18:06
  • This could also be for a fairly simple reason that the same factors (poor family) frequently cause both chances of lead exposure AND subsequent criminality. Did the studies mentioned control for that?
    – user5341
    Jan 4, 2013 at 18:28
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    Kinda like how this chart explains global warming?
    – Sam I Am
    Jan 4, 2013 at 22:59
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    FWIW, I've also heard that there is a correlation between legal abortion and declining crime rates -- fewer unwanted children, better childhood, better adjusted adults.
    – Chris Cudmore
    May 16, 2013 at 20:35

2 Answers 2

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Per Wayne Hall in 2013, "lead exposure in childhood may have played a small role in rising and falling crime rates in the USA but it is unlikely to account for the very high percentage of the decline suggested by the ecological studies. We need more cohort studies in environments where lead exposure remains high, particularly in developing countries. The results of these studies could inform epidemiological modelling to estimate the likely population level effects on crime of observed reductions in lead exposure. This modelling would test the plausibility of the lead hypothesis. So too would controlled evaluations of the costs and benefits of reducing environmental lead exposure in high crime inner city areas or moving highly exposed populations from areas of high lead burden."

But the evidence is not sufficient to conclude that variations in environmental lead exposure in childhood over the past 50 or so years in the USA explain, first the rise, and then the decline in crime rates. The major reason for doubt is that the associations in ecological studies are much stronger (explaining 60–90% of the variation in crime rates) than the weaker relationships in the cohort studies (that explain less than 1% of the variance in offending). Lead exposure in childhood may have played a small role in rising and falling crime rates in the USA but it is unlikely to account for the very high percentage of the decline suggested by Nevin and Reyes.

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I agree, what kind of evidence do you need? There are studies demonstrating changes in the brains (MRI's included) of Cincinnati Lead Study participants that were monitored over a twenty year or so period to prove exactly what areas of the brain are being affected. There are studies documenting areas most affected by lead and corrosponding crime. How many studies are needed to prove causation? What type of study could be done in this case safely?

Also, in terms of other health hazards, where are studies proving causation? It is accepted that aspartame contributes to degenerative disease, but show me studies that are any more decisive than the handfuls of studies done on various aspects of lead and its contribution to criminality.

http://pic.plover.com/Nevin/Nevin2007.pdf

http://www.nber.org/papers/w13097.pdf?new_window=1

http://www.ricknevin.com/uploads/Nevin_2000_Env_Res_Author_Manuscript.pdf

http://www.ricknevin.com/uploads/4-6_Prevent_Childhood_Lead_Poisoning.pdf

http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.0050112

http://ksj.mit.edu/tracker/2013/01/lead-and-crime

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    Does the correlation stand in other countries (different demographics/policies, etc.)?
    – Larry OBrien
    Feb 11, 2013 at 20:04
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    Proving that lead causes criminal behaviour does not exclude other concurrent and possibly much more significant causes. Even the last of your sources says so clearly: "But in this latest story, he goes much farther in embracing lead as the primary cause of violent crime, so much farther that that it's worth asking whether leaded gasoline, as he asserts, does explain as much as 90 percent of the rise and fall of violent crime. Does it trump drugs, poverty, urban gang warfare, education, (cont...)
    – Sklivvz
    Feb 11, 2013 at 20:32
  • (...) and other such issues to the point that they account for a bare ten percent of the crime statistics? That's a harder case to make, partly because as Drum himself notes correlation is not causation: the fact, for instance, that falling crime follows a pattern of falling lead exposure doesn't rule out many other influences."
    – Sklivvz
    Feb 11, 2013 at 20:32
  • You are reading incorrectly. He states that it is responsible for 90% of the fall of crime in that period, not 90% of crime to begin with. Read the studies. There are many variables that are accounted for.
    – Jaime
    Feb 12, 2013 at 16:54
  • ncbi.nlm.nih.gov/pubmed/22484219 This is a perfect example of what 90% means where as reading 90% without context seems impossible
    – Jaime
    Feb 12, 2013 at 17:00

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