Association for Public Policy Analysis & Management

In recent years, policymakers and citizens alike have turned their attention to the social harms of mass incarceration. It has been suggested that spending on both prisons and police have been excessive. After all, even if police affect crime through deterrence, given that police make arrests, they must also incapacitate offenders and therefore contribute to mass incarceration.

The extent to which -- and whether -- more police lead to more incarceration is an empirical question. If the deterrence effects of police are sufficiently large relative to incapacitation effects, then it is possible that more law enforcement could lead to both a reduction in crime and imprisonment. Can investments in law enforcement generate such a "double dividend?'' This idea has gained traction in policy circles and formed the basis for a recent and prominent article in the City Journal by George Kelling and William Bratton.

However, despite the fact that the effect of law enforcement on incarceration has broad implications for how public safety resources are allocated, this quantity has not been estimated in the literature. The closest research is that of Owens (2013) who, intriguingly, finds little evidence that arrests increase with police hiring. While this evidence suggests only a modest scope for police to generate large incapacitation effects, we argue that an analysis of arrests is insufficient to draw a conclusion about the effect of police on new prison commitments as the rate at which arrests convert into prison spells depends on many factors including the type of arrest, strength of the evidence, the dynamics of plea bargaining and the de jure and de facto sentencing regimes.

This research addresses the incredibly important and yet understudied question of whether investments in law enforcement lead to an increase in a state's incarceration rate. Using panel data, we estimate the effect of increases in police expenditures on actual and expected prison commitments. In order to isolate plausibly exogenous variation in spending on law enforcement, we appeal to an old idea in the literature that we argue remains credible -- that investments in law enforcement tend to move in accordance with investments in fire safety (Levitt 2002). The intuition for this relationship is straightforward -- institutional details such as the power of public sector unions, citizen tastes for government services and the predilection of politicians to ``provide spoils'' to their electorates suggest that police and fire safety budgets might covary. Empirically, we demonstrate that this is the case.

While estimates are imperfectly precise, the available data suggest that the effect of police spending on new prison commitments is likely to be negative and is unlikely to be large and positive. Even using an extraordinarily pessimistic estimate of the effect of police spending on prison commitments, the premise that increases in spending on law enforcement drive mass incarceration is extraordinarily unlikely to be true. Thus, we suggest that society may, in fact, be able to have it's cake and eat it too.