For journalists, researchers and the general public, the Centers for Disease Control and Prevention serves as an authoritative source of information about Americans’ health, including estimates of how many people are killed or injured by guns. The agency’s most recent figures include a worrying uptick: Between 2015 and 2016, the number of Americans nonfatally injured by a firearm jumped by 37 percent, rising from about 85,000 to more than 116,000. It was the largest single-year increase recorded in more than 15 years.