A natural experiment study of the effects of imprisonment on violence in the community.

One of the goals of imprisonment is to reduce violence1. Although imprisonment has risen dramatically since the 1970s, its effects on future violent crime are poorly understood2. This study's objective was to examine the effect of imprisonment on violent crime in the community among individuals on the policy margin between prison and probation sentences. Drawing on data from a population-based cohort of individuals convicted of a felony in Michigan between 2003 and 2006 (n = 111,110) and followed through June 2015, we compared the rates of commission of violent crime committed by individuals sentenced to prison with those of individuals sentenced to probation using a natural experiment based on the random assignment of judges to criminal cases. Being sentenced to prison had no significant effects on arrests or convictions for violent crimes after release from prison, but imprisonment modestly reduced the probability of violence if comparisons included the effects of incapacitation during imprisonment. These results suggest that for individuals on the current policy margin between prison and probation, imprisonment is an ineffective long-term intervention for violence prevention, as it has, on balance, no rehabilitative or deterrent effects after release.