The basic question is, why? Did mothers of more crime-prone children abort, or were there simply fewer children overall, or was some other factor at play? To answer this question, the study authors collected data on births and later-in-life crime levels and rates, then used those data to examine how being born immediately before or immediately after a change in law changed a given birth cohort’s propensity to commit crime. Because they had month-level birth data, they were able to look precisely at the effect of the timing of each change.

The results are surprising: while crime levels rose following criminalization and dropped following legalization, overall crime rates — i.e. crimes per number of cohort members — remained constant. This finding is clear over a number of different crime categories, and persists even given a variety of statistical controls.

“Our main finding is that abortion policy in Romania has had a large and significant impact on the number of crimes and hospitalizations for crime-related behaviors,” the authors explain. “But this impact is proportionate to the change in the size of the population, such that there is no significant effect on crime or hospitalization rates. Moreover, this pattern of significant level but insignificant rate effects is seen across multiple crime outcomes and opposing reforms, increasing the external validity of these results.”