Background Mass shootings are common in the United States. They are the most visible form of firearm violence. Their effect on personal decisions to purchase firearms is not well understood. Objective To determine changes in handgun acquisition patterns after the mass shootings in Newtown, Connecticut, in 2012 and San Bernardino, California, in 2015. Design Time-series analysis using seasonal autoregressive integrated moving-average (SARIMA) models. Setting California. Population Adults who acquired handguns between 2007 and …