Does carrying a gun make you safer? Does it make other people safer? Millions of Americans who pack heat think so, and 33 states with “right to carry” laws permit them to tote a gun. But a long-range study released by the National Bureau of Economic Research found that these states would have had less violent crime had they restricted gun-carrying. John J. Donohue, a Stanford law professor and economist, is a lead author of the analysis, which used more than 30 years of crime statistics and a novel algorithm: Researchers identified states whose crime rates paralleled those of states like Texas before it passed a “right to carry” law, and came up with models — called synthetic states — to look at before-and-after violent crime in right-to-carry states and non-right-to-carry “synthetic” states. It’s comparing apples and virtual apples, and Donohue – who’s also an expert witness in a right-to-carry lawsuit against the state of California — concluded that gun-toting indeed makes a difference in violent crime: it can increase it, by as much as 15%.