At the heart of law and economics are people like John Donohue, a Stanford law professor who has spent years researching the real-world effects of laws on crime, guns and abortion. A profile last week highlights Donohue’s work, which suggests permissive concealed carry laws increase violent crime, that gun permit-holders hardly ever thwart mass shootings and that abortion is a big reason for the precipitous drop in crime throughout the 1990s.