Before I started researching gun deaths, gun-control policy used to frustrate me. I wished the National Rifle Association would stop blocking common-sense gun-control reforms such as banning assault weapons, restricting silencers, shrinking magazine sizes and all the other measures that could make guns less deadly.

Then, my colleagues and I at FiveThirtyEight spent three months analyzing all 33,000 lives ended by guns each year in the United States, and I wound up frustrated in a whole new way.