A second thing I think we could say we've learned -- and this may not come as a surprise either -- but if you're having changes in fertility of that magnitude, the characteristics of the children who are born are different than they otherwise would have been. It's very difficult to believe that the women who chose to have an abortion and didn't have a child because of that were randomly selected in the population. And so, because of that, the lack of random selection, the children who were born were different than the ones who would have been born otherwise.

Living standards of children growing up were very different as a result. Fewer children grew up living in poverty, fewer children grew up in single parent households, fewer children grew up in households headed by welfare recipients. In some sense, you can think about following that cohort's path through life into things like educational attainment, labor market outcomes. You observe increases in college graduation, lower rates of welfare use for the children themselves, reduced likelihood of becoming a single parent themselves. These are outcomes for the children who were born in the early 70s that we observe 20 years later, that we observe for the cohort as a whole. Because it's a different group of children born relative to those who would have been otherwise. That's not to say that's a good thing, that's just what happened.

Is it fair to call those economic benefits?

I think this is an incredibly sensitive topic, so I want to avoid using terms like ... "benefit." Different children were born. An empirical fact is that the ones who were born are the ones who were more likely to have better economic outcomes. The value judgment on whether that's a good thing or a bad thing is something I don't want to get into.

What about women in particular? How did legalizing abortion affect their economic standing?

It turns out getting direct evidence of that is not such an easy thing to do. While there certainly are indications that women's economic outcomes were directly improved by abortion legalization, I wouldn't necessarily say that's the sort of thing that research has conclusively proven. We are clearly able to find support for the notion that their fertility was affected. And you certainly could imply from that if you're better able to time giving birth, you're better able to make other sorts of decisions that would improve your economic well being. Direct evidence of that is a little bit limited. There is some work that shows educational attainment and labor market outcomes have improved, but it's a little bit limited.

Why is that research so limited?

Statistically, it's a very hard thing to find support for. It's a statistical issue as opposed to an economic issue.

In some sense, what economists are always trying to do when we find evidence for something -- you're trying to look for something that looks like an experiment. Where one group is exposed to something and another group wasn't, and what was the difference in the outcomes. That works really well when thinking about a fertility decision when the law changes and not so well when you're thinking about these longer term decision-making processes.