Kevin Drum asks a good question in his post How Many Cops Does New York City Need? First note that violent crime has been dropping since around 1990 (see his graph copied here for examples). In particular for NYC:
The per capita number of police officers increased by about 10 percent through 2000 and then declined by about 20 percent through 2018. That’s nearly flat over the entire period. Violent crime, by contrast, plummeted 60 percent from its peak in 1990 through 2000 and then declined another 40 percent through 2018. That’s a total decrease of nearly 80 percent between 1990 and 2018.
Violent crime has decreased even though the per capita number of cops has been nearly flat. So, why did crime decrease? There is overwhelming evidence that removing lead emissions from cars is the main driver of crime decline. I strongly encourage you to read Drum’s 2018 summary of the evidence.
So, why doesn’t anyone talk about lead and crime?
The second problem is among activists on both left and right who have their own pet theories. On the left, we tend to blame poverty, institutional racism, poor schooling, lousy housing, and so forth. On the right, the favorite targets are the breakdown of the family, too few cops, too few prisons, drugs, the decline of religion, and so forth. There is very little convincing evidence for any of this, while lead poisoning explains everything. But if lead poisoning is the answer, then everyone has to give up their pet theories about what happened between 1960 and 2010. That’s a tough ask.
We forget that there was a lot of violent crime in the 1980s. It had an impact on society in many ways. But, we are past that and removing lead from the environment is a permanent fix to the violent crime wave of the past. This should allow us to think differently about societal needs for policing.
The Drum post has two other graphics. The Statistics Projects page has the relevant lead and crime data.