Law & Order
Eleven More Cops, One Fewer Murder

How much do police reduce crime? A recent paper by Princeton University PhD candidate Steven Mello uses evidence from COPS, a federal grant program for local police-hiring that was re-activated as part of the stimulus package, to develop some estimates. The results are impressive: Each extra officer seems to have a significant impact on rates of property and even violent crime. From his conclusion:

My estimates suggests that an additional officer is associated with 1.39 fewer robberies, 9.6 fewer larcenies, and 3.5 fewer auto thefts. I also find evidence of a sizable effect of police on murder – the coefficient in the main specification is statistically significant and implies that one murder per year can be prevented by hiring eleven officers.

Much of the debate over criminal justice policy focuses on sentencing and incarceration rates, with reformers calling for shorter sentences and law-and-order advocates warning against releasing criminals. But Mello’s data are a reminder that while sentencing matters, making it more likely that offenders are caught in the first place is the most effective way of controlling crime.

While America has one of the highest incarceration rates in the world, it has relatively few police officers per capita. The economist Alex Tabarrok has argued that we have things backwards: That a system of “swift and certain” punishment—one with shorter sentences, but where a robust police force solved a higher percentage of cases—would reduce crime more effectively at less cost.

Of course, a push to hire more police would encounter some resistance, given the spate of high-profile controversies over police shootings. But at a time when Americans are deeply concerned about rising crime rates and overall support for police officers is at historically high levels, a hire-more-cops policy is likely to be quite popular. Policymakers looking for ways to further control crime and violence in America’s cities should take note of Mello’s work.

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