More Guns, More Time: Using Add-on Gun Laws to Estimate the Deterrent Effect of Incarceration on Crime

Abstract

Knowing the magnitude of the deterrent effect of incarceration on crime is crucial to optimal policy setting. In this paper I make use of sentence enhancements in gun robbery sentence lengths caused by add-on gun laws to attempt to estimate this impact. Since defendants subject to add-ons would be incarcerated in the absence of the law change, the short-term effect will be solely deterrent. I take advantage of the temporal variation in the passage of these laws in different states to identify the causal impact of the law change. I find that add-on gun laws result in a significant reduction in gun robberies, approximately 5% within the first three years of passage, for the average add-on gun law. The results are robust to a number of tests, and do not appear to be due to a large spillover to other types of crime.