LEVITT: So it’s not that easy to convince people that there’s a causal impact of legalized abortion on crime, because this is certainly not a setting in which I’m ever going to be allowed to, say, run a randomized experiment in which I decide who does or doesn’t get abortions. Instead, what we have to do by necessity is to look at a collage of evidence. So a bunch of different, all quite imperfect sources of variation, that allow us to get some sense of whether there might be some causality between legalized abortion and crime.