The Deterrent Effect of Capital Punishment: Evidence from a "Judicial Experiment"

Does capital punishment deter capital crimes? We use panel data covering the fifty states duringthe period 1960-2000 period to examine the issue. Our study is novel in four ways. First, we estimate the moratorium's full effect by using both pre- and postmoratorium evidence. Second, we exploit the moratorium as a judicial experiment to measure criminals' responsiveness to the severity of punishment; we compare murder rates immediately before and after changes in states' death penalty laws. The inference draws on the variations in the timing and duration of the moratorium across states provide a cross section of murder rate changes occurring in various time periods. Third, we supplement the before-and-after comparisons with regression analysis that disentangles the impact of the moratorium itself on murder from the effect on murder of actual executions. By using two different approaches, we avoid many of the modeling criticisms of earlier studies. Fourth, in addition to estimating 84 distinct regression models - with variations in regressors, estimation method, and functional form - our robustness checks examine the moratorium's impact on crimes that are not punishable by death. Our results indicate that capital punishment has a deterrent effect, and the moratorium and executions deter murders in distinct ways. This evidence is corroborated by both the before-and-after comparisons and regression analysis. We also confirm that the moratorium and executions do not cause similar changes in non-capital crimes. The results are highly robust.