Do right-to-carry laws deter violent crime?

John R. Lott and David B. Mustard conclude that right-to-carry laws deter violent crime. Our reanalysis of Lott and Mustard's data provides no basis for drawing confident conclusions about the impact of right-to-carry laws on violent crime. We document that their results are highly sensitive to small changes in their model and sample. Without Florida in the sample, there is no detectable impact of right-to-carry laws on the rate of murder and rape, the two crimes that by the calculations of Lott and Mustard account for 80 percent of the social benefit of right-to-carry laws. A more general model based on year-to-year differences yields no evidence of significant impact for any type of violent crime, As a result, inference based on the Lott and Mustard model is inappropriate, and their results cannot be used responsibly to formulate public policy.