This morning, I encountered two studies examining guns and background checks. The first examined school shootings, finding that 154 shootings occurred between 2013 and 2015. Using newspaper articles from that time period, as well as publicly available data, they found that school shootings were less likely to occur in states with background check laws, higher expenditures on mental health care, and higher expenditures on K-12 education.
Based on these data, we might be able to conclude that if guns are more difficult to get (i.e., background check), they're less likely to be used for school shootings. This would suggest background checks are a good thing - as is mental health treatment and education, of course. Unfortunately, the second study I read was based on a national survey of how many people were able to purchase guns without a background check. And they found that 22% of people surveyed were able to purchase a gun without such a check. When you look at private sales between individuals (which includes gun shows), that number jumps to 50%. Even in states that regulate private gun sales, 26% said they were able to purchase a gun without a background check.
As the article points out, the previous figure from 1994 data suggested that 40% were able to purchase a gun without a background check. So these new data suggest improvement. But considering the lives that could be saved from background checks, that's still a lot of guns that could be in the hands of people who really shouldn't have guns in the first place.