A July study of more than 20 states that since 2015 let owners carry concealed handguns without first getting a license estimated violent crime rose 7 percent in the 12 months after those laws were adopted. The increase started soon after passage or several months before the laws took effect. Firearm aggravated assaults drove a 12 percent jump, property crime showed no drop, police enforcement of weapons violations fell 22 percent, and stolen-firearm reports rose modestly.

An earlier Connecticut permit-to-purchase paper had claimed a 40 percent gun-homicide drop by comparing the state with a blend of Rhode Island, California and other places rather than its own prior years or the nation. The same data later showed the real rate more than 40 percent above that blend within a few years.