Does increasing police strength deter more crime? Some studies have found apparent negative effects of police manpower levels on crime rates, and the most common explanation of such findings is that greater police strength increases perceptions of arrest risk, thus reducing crime via general deterrence mechanisms. The authors directly tested this hypothesis by estimating the association between survey respondents’ perceptions of arrest risk and the level of police strength prevailing in the counties where they live. No relationship between the number of police officers per capita and perceptions of the risk of arrest was found, suggesting that increases in police manpower will not increase general deterrent effects and decreases will not reduce these effects. The authors also considered the possibility that police manpower levels influence the number of criminals incarcerated, and thus affect crime rates via the incapacitative effects of incarceration, but concluded that such an effect is unlikely. These findings point to a need to reconsider previous interpretations of findings as supportive of a deterrent effect of increased police manpower on crime rates.