Estimating the effect of U.S. concealed carry laws on homicide: A replication and sensitivity analysis

Abstract

In this article, we perform sensible robustness checks and estimation techniques that are broadly applicable to researchers studying the effects of concealed carry laws and apply them to recent work by Moody and Lott (2022). While Moody and Lott claim to have found that shall-issue and permitless-carry laws reduce homicide using data ending in 2014, our event-study analysis demonstrates that their model violates the conditional parallel-trends assumption. Additionally, applying methodology from Broderick et al. (2021), we show Moody and Lott’s results are highly sensitive to the removal of a small number of observations. We examine and reject Moody and Lott’s hypothesis that early- and late-adopting “shall-issue” states experienced different outcomes through sensitivity testing of their early–late threshold and applying the Goodman-Bacon (2021) decomposition. Following De Chaisemartin and d’Haultfoeuille (2020), we show Moody and Lott’s results are biased by heterogeneous treatment effects. Overall, our results highlight the importance of conducting principled validity and sensitivity checks before introducing outlier estimates into the empirical literature.