In the two weeks after a gun show is held in Nevada, injuries and deaths involving firearms jump by 69 percent -- in neighboring areas of California.
However, when gun shows occur in California, the state does not experience an increase in firearm-related trauma over the next fortnight.
The findings, published Monday in the Annals of Internal Medicine, show that state gun laws have a measurable effect on public safety, especially when it comes to gun shows, the study authors wrote.
More than 4,000 gun shows are held in the United States each year, and experts estimate that they're responsible for 4 percent to 9 percent of the nation's firearms sales. When these sales are made by federally licensed gun dealers, would-be buyers are subject to a background check. But in some states, unlicensed sellers at gun shows don't have to follow the same rules.
California, which has some of the strictest gun laws in the country, requires background checks even at gun shows. Nevada does not.
Ellicott Matthay, a public health researcher at the University of California, Berkeley, and her colleagues recognized this as an ideal scenario for testing the effects of state laws regarding gun show sales.
The researchers scoured gun show listings in a magazine called the Big Show Journal. Altogether, they tallied 275 such shows in Nevada and 640 shows in California between Jan. 1, 2005, and Dec. 31, 2013. Then they identified regions in California that were within a one-hour drive of a California gun show or a two-hour drive of a Nevada gun show.
(Interesting fact: Most California residents could have driven to a gun show in 60 minutes or less at least once every few weeks.)
Next, the researchers used state health data to compare the number of gun injuries -- both fatal and nonfatal -- for each of the study regions in the two weeks before and two weeks after the nearby show. When the show was in California, the "after" period began 10 days after the show's opening day, because buyers were subject to the state's 10-day waiting period.
Altogether, 15,000 Californians were injured or killed by firearms in the two weeks before California gun shows, as were 14,893 in the two weeks after those gun shows. In the before-and-after comparison, the rate of firearm injuries and deaths remained essentially flat, at about 1.3 per 100,000 people, the researchers found.