Growing restrictions on the right to an abortion have revived talk of what many still regard as a highly controversial theory. It holds that the legalization of abortion in 1973 reduced the number of unwanted children, who might have been at higher risk of committing serious crimes. And that explained the sharp drop in the crime rate that started in the early 1990s.

This theory, which rubbed many nerves raw as racist, occupied a chapter in "Freakonomics," a 2005 bestseller. "There is a long lag between abortions being performed and the affected cohort reaching the age at which crime is committed," one of the authors, University of Chicago economist Steven Levitt, recently wrote in the Economist. "It is rare 鈥 almost unprecedented 鈥 in academic economics to be able to make a testable prediction and then to go back and actually test it decades later."