A theory regarding the effect of legalized abortion on crime (often referred to as the Donohue–Levitt hypothesis) is a controversial hypothesis about the reduction in crime in the decades following the legalization of abortion. Proponents argue that the availability of abortion resulted in fewer births of children at the highest risk of committing crime. The earliest research suggesting such an effect was a 1966 study in Sweden. In 2001, Steven Levitt of the University of Chicago and John Donohue of Yale University argued, citing their research and earlier studies, that children who are unwanted or whose parents cannot support them are likelier to become criminals. This idea was further popularized by its inclusion in the book Freakonomics, which Levitt co-wrote.
Critics have argued that Donohue and Levitt's methodologies are flawed and that no statistically significant relationship between abortion and later crime rates can be proven.[1][2][3] Criticisms include the assumption in the Donohue-Levitt study that abortion rates increased substantially since the 1973 Supreme Court case Roe v. Wade; critics use census data to show that the changes in the overall abortion rate could not account for the decrease in crime claimed by the study's methodology (legal abortions had been permitted under limited circumstances in many states prior). Other critics state that the correlations between births and crime found by Donohue–Levitt do not adequately account for confounding factors such as reduced drug use, changes in demographics and population densities, or other contemporary cultural changes.
Part of the problem is the long and uncertain time lag between cause and effect. If increased abortion rates reduce crime among the cohort of children born during a particular year, the effect would only become apparent ten to twenty years later. To isolate the effect of abortion on crime, it is necessary to control for other factors that affect birth cohorts (e.g., relative cohort size or the prevalence of crime during childhood) and those that have immediate effects in later years (e.g., wage or incarceration rates).[4]
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Based on an analysis of the past findings, it is possible that some portion of the decline in 1990s could be attributed to the legalization of abortion. However, there is also robust research criticizing this theory.
While the data from some countries are consistent with the DL hypothesis (e.g. Canada, France, Italy), several countries' data show the opposite correlation (e.g. Denmark, Finland, Hungary, Poland). In other cases crime was falling before legalization and does not decline any more quickly (twenty years) after legalization (e.g. Japan, Norway).
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