Terror Alerts and Crime

The question of how the amount of policing affects the crime rate is often asked and investigated. The main problem of course is that the two variables of police levels and crime rates are determined simultaneously so one would naturally have a hard time disentangling the direction of causation. Do more police lower the crime rate or do more police increase the crime rate (since we observe more police in places with higher crime rates).

A recent article from the Journal of Law and Economics estimates the impact of police presence without having to suffer the problem of simultaneity. What the authors did was exploit the natural experiment provided by changing terror alert levels and they concentrated on one city which is Washington DC. The higher terror alert levels (a variable that is not related to everyday crime rates) leads to more police presence especially in the National Mall area of Washington DC this increased police presence it turns out leads to 2.6 less crimes per day in the National Mall area. So there, a clearer evidence that increase police activity lowers crime.