Persistent claims have been made that expanding background checks to include any private transfers of guns would reduce mass public shootings. Yet, this is the first study to systematically look to see if that is true. In fact there is no evidence that these laws reduce the risk of these attacks. Examining all the mass public shootings in the US from 2000 through 2015, we find that states adopting additional background checks on private transfers they see a statistically significant increase in rates of killings (80% higher) and injuries (101%) from mass public shootings. There is not one mass public shooting that occurred over that period where these checks would have prevent from occurring.
You can read the paper to judge for yourself the statistics.