CLAYTON CRAMER: Background Checks And Murder Rates. “What is the statistical evidence of the effects of state mandatory firearms background check laws on murder rates? For states that adopted or repealed such laws after 1960 (when consistent and high quality murder rate data becomes available), an interrupted time series analysis shows that five out of nine states have statistically significant changes in murder rates, with three having higher murder rates during the background check period, and two having lower murder rates. Of the four states with statistically insignificant changes in murder rates, two had higher murder rates during the background check period, and two had lower murder rates during the background check period.”