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.

But the gun injury estimate is one of several categories of CDC data flagged with an asterisk indicating that, according to the agency’s own standards, it should be treated as “unstable and potentially unreliable.” In fact, the agency’s 2016 estimate of gun injuries is more uncertain than nearly every other type of injury it tracks. Even its estimates of BB gun injuries are more reliable than its calculations for the number of Americans wounded by actual guns.

An analysis performed by FiveThirtyEight and The Trace, a nonprofit news organization covering gun violence in America,1 found that the CDC’s report of a steady increase in nonfatal gun injuries is out of step with a downward trend we found using data from multiple independent public health and criminal justice databases. That casts doubt on the CDC’s figures and the narrative suggested by the way those numbers have changed over time.

“For those of us who are doing this kind of research, it’s disconcerting,” said Priscillia Hunt, a researcher at the RAND Corporation, a nonprofit research organization. “With the CDC, there’s this general assumption that they are reliable and have good data.” Hunt herself cited the estimates in the introduction of a policy paper she published last year. “It feels like a gotcha moment for people who’ve used it,” she said.

In the case of the CDC’s 2016 gun injury estimate, the confidence interval indicates there is a 95 percent chance that the true number of total gun injuries falls somewhere between a low of 46,524 and a high of 186,304.6 “Basically, the confidence intervals are enormous,” said Hemenway, the Harvard Injury Control Research Center director. “So you have no idea about trends.”

featureless wrote: Thu Oct 04, 2018 6:24 pm A low of 46,524 and a high of 186,304? That's one hell of a range!

The consensus among the researchers interviewed by The Trace and FiveThirtyEight is that the rise in the CDC’s gun injury estimate is likely caused by some hospitals in the sample treating more gun injuries than others. “If you have hospitals in communities that have a lot of firearm injuries, it’s going to change the estimates in a very significant way,” said Guohua Li, editor-in-chief of the peer-reviewed medical journal Injury Epidemiology and director of Columbia University’s Center for Injury Epidemiology and Prevention.

For now, external research supports our suspicions. A 2017 study co-authored by Phil Cook at Duke University and published in the American Journal of Public Health established how heavily hospital selection can skew injury estimates in the NEISS. Cook said the research found that the addition of just five gun-treatment hot spots to the pool of hospitals in the CDC data accounted for much of the apparent increase in nonfatal gunshot injuries from assaults. When Cook adjusted his model to account for the distortion from these hot spots, the trend in nonfatal shootings from year to year appeared to be flat.

“No one should trust the CDC’s nonfatal firearm injury point estimates,” said David Hemenway, director of the Harvard Injury Control Research Center.