Leaded gas came out in the 1970s. Crime fell in the 1990s. The press credited the police.

What fell, and when.

The FBI's violent crime rate (murder, rape, robbery, aggravated assault per 100,000 people) was 161 in 1960, 364 in 1970, 597 in 1980, and 758 at the 1991 peak. It then dropped every year through 2000, to 506, and kept sliding to 379 by 2019. In 2020 it was 388.

The lead side of the picture is a plateau followed by a cliff. American toddlers born between 1930 and about 1976 carried blood lead around 16 micrograms per deciliter, from lead paint first and then paint plus gasoline. Our own NHANES analysis puts toddlers born 1973 to 1977 at a mean of 16.4. Toddlers born 1986 to 1990 were at 4.1. Toddlers born 2016 to 2020 were at 0.6. The number did not climb through mid-century. It sat high and flat for two generations and then fell off a shelf once the EPA began removing lead from gasoline in the mid-1970s.

That shape matters for what can and cannot be claimed. A flat plateau cannot explain a rise. The 1960s and 1970s climb in crime happened while childhood lead was already high and not changing, so it has other causes. What lead can explain is the fall. The first cohorts with clean childhoods were born around 1977 to 1980. They reached the peak offending ages, roughly 18 to 24, between 1995 and 2004. That is when the crime rate fell hardest.

The two lines are not the same shape on the way up. Crime rose from 1960 to 1991 while the shifted lead line stayed flat. They are the same shape on the way down. By the time the 1988 births turn 20, in 2008, childhood lead for the incoming cohort is under 4 and the crime rate has given back most of the climb.

The state-by-state test.

Jessica Wolpaw Reyes, an economist at Amherst, published the analysis that turned this from a national overlay into something closer to an experiment. States did not remove lead from gasoline at the same pace. The federal phase-down set targets in grams of lead per gallon, but the fuel mix, refinery behavior and vehicle fleets differed by state, so children in some states saw their blood lead fall years before children in others.

Reyes built a panel of state-year observations from 1985 to 2002, matched each state's violent crime rate to the gasoline lead exposure of the cohort that was young in that state two decades earlier, and controlled for the other explanations on offer at the time: police per capita, prison population, the effective abortion rate from Donohue and Levitt's 2001 paper, beer consumption, crack, unemployment, income, and demographics.

An elasticity of 0.8 means that a 10% fall in a cohort's childhood lead exposure predicts an 8% fall in that cohort's violent crime rate as adults. Reyes then asked what that implied for the period from 1992 to 2002, when violent crime fell by about a third. Her answer is the number this page is built on: the fall in gasoline lead alone would have produced a 56% decline in per-capita violent crime over those ten years.

Two things about that number need to be said plainly. First, 56% is larger than the total observed drop of 34%, so it is not "56% of the decline." It is the drop her model attributes to lead, sitting alongside a 29% drop she attributes to abortion legalization and a 23% drop from police, prisons, beer and crack, with a large unexplained residual pushing the other way. Second, the result held for violent crime and not for property crime, and the murder result was not stable when New York and the District of Columbia were included. The paper reports both limits itself.

The same design answers the objection that a national overlay cannot: if the crime drop were caused by something national (a federal sentencing law, the business cycle, cable television), it would not arrive earlier in the states that cleaned up their gasoline earlier. It did. The incarceration page covers the individual-level cohort studies (Wright 2008, Needleman 1996) and the mechanism in the prefrontal cortex. This page stays on the population question.

Nine countries, six cities, one lag.

Rick Nevin published the first version of the overlay in Environmental Research in 2000, showing that long-term U.S. trends in gasoline lead were remarkably consistent with subsequent changes in violent crime. In 2007 he repeated it for Britain, Canada, France, Australia, Finland, Italy, West Germany and New Zealand. In each country the best-fit lag between preschool blood lead and later crime lined up with the peak offending age for that offense: shorter for burglary, longer for violent crime. None of those countries had Rudolph Giuliani, CompStat, three-strikes laws or an American crack market. They had leaded gasoline, they removed it, and their crime rates fell a generation later.

Howard Mielke and Sammy Zahran took the question down to the city in 2012. They regressed annual FBI aggravated assault rates in Chicago, Indianapolis, Minneapolis, San Diego, Atlanta and New Orleans against each city's own vehicle lead emissions 22 years earlier.

New Orleans was the extreme case. The rise and fall of air lead there, 10,179 metric tons over the period, explained 85% of the year-to-year movement in its aggravated assault rate two decades on. Cities that emitted more lead had higher assault peaks, with the same 22-year gap in every city.

What our own numbers say, and the ceiling we hold them under.

This site runs its own cohort correlations. We take a birth cohort's childhood blood lead from the integrated index above, follow it forward to the age at which a given behavior peaks, and compare the outcome rate in that year to the cohort's childhood exposure. The results for crime:

The bound we cite against ourselves comes from Anthony Higney, Nick Hanley and Mirko Moro, who published the first meta-analysis of the lead-crime literature in 2022. They pooled 542 estimates from 24 studies and found that the published effect sizes are inflated by publication bias. Corrected, their mean elasticity is 0.09, far below Reyes's 0.8, and their conclusion is that lead abatement accounts for somewhere between 7% and 28% of the fall in U.S. homicide. Their sentence is worth taking at face value: lead increases crime, but does not explain the majority of the fall in crime observed in some countries in the 20th century.

So the honest range runs from Higney's 7% to Reyes's estimate, and the truth for violent crime as a whole is probably in between. Even at the bottom of that range, a removed toxicant explaining 7% of the largest crime decline in American history would be a front-page finding in any other field. In criminology it is a footnote.

Why the press credited the police.

The 1990s crime drop was covered as it happened, and the people available to explain it were police chiefs, mayors, prosecutors and criminologists. New York's decline was the most visible, and New York had a mayor and a police commissioner who claimed it. Broken-windows policing and CompStat had names, faces and press offices. The abortion hypothesis had Freakonomics. The crack story had the reporters who had covered the crack years.

Lead had Rick Nevin, a housing economist working on a HUD cost-benefit analysis, and later an Amherst economist publishing in a Berkeley Electronic Press journal. Neither had a beat reporter. The finding was about children exposed twenty years earlier, so there was no one to interview at the scene, no policy to praise or attack that week, and no institution whose job it was to keep saying it.

Each of the standard explanations also fails a test that lead passes. Policing reforms were local, so they cannot explain why the fall was national. The prison build-out was American, so it cannot explain Canada or Finland. The abortion hypothesis is American too, and Reyes's own regression puts its contribution at about half of lead's. Crack burned out in specific cities in specific years. The lead phase-out happened in every industrial country within about a decade, and the crime declines followed in every one of them on the same lag. The policing story has never had an answer for that.

Kevin Drum wrote the piece that put all of this in one place, "America's Real Criminal Element: Lead," in the January/February 2013 issue of Mother Jones. It was widely read and widely linked, and it is still what most people who know the hypothesis are citing when they bring it up in a comment thread. The response from the rest of the press was to cite it, once, and go back to the frame they already had. Crime-drop explainers published since then still list policing, incarceration, demographics, the economy and abortion, and put lead near the bottom or leave it out.

Some of that is how disciplines work. Criminology has its own journals and funders, environmental health has different ones, and the criminologists are who the crime reporters call.

The fair objection.

The most careful public discussion we found of this question was a long comment in r/AskHistorians answering why crime fell in the 1990s. The writer's first point was that the drop happened in many countries at once, under different and sometimes opposite policies, so any explanation that only works in one country is suspect. Their second was that people credit whichever policy they already favored. Their third was that the lead hypothesis has been tested at the local, state, national and international level and in birth cohort studies, with more consistent results than the abortion hypothesis, while the range of published estimates for lead's share is wide.

That is a fair reading, and it is the reading this page takes. The specific criticism of Nevin's work is that he chose the lag for each outcome by best fit, which lets the analyst find a lag that works. Nevin says as much in his own abstract. Reyes's design does not have that freedom. The exposure is fixed by the age of the cohort and the year the state's gasoline changed, and the crime outcome is whatever that cohort did two decades later. The lag is not fitted, it is given. That is why her paper, and not Nevin's, is the one to cite when someone says correlation is not causation.

The remaining objection is Higney's, and it is the one that stands: the literature as a whole overstates the effect, and the real share is smaller than the overlays suggest. We accept that. A bounded share of 7 to 28% of the homicide decline is still a share of the homicide decline that a specific policy produced, on a specific timetable, in a specific set of children who are now in their forties and fifties.

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