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.
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.
The 1972 Rockefeller Commission on "Population and the American Future" cites a 1966 study which found that children born to women who had been denied an abortion "turned out to have been registered more often with psychiatric services, engaged in more antisocial and criminal behavior, and have been more dependent on public assistance.
The unwanted children were more likely to grow up in adverse conditions, such as having divorced parents or being raised in foster homes and were more likely to become delinquents and engaged in crime.
Donohue and Levitt suggest that the absence of unwanted children, following legalization in 1973, led to a reduction in crime 18 years later, starting in 1992 and dropping sharply in 1995.
[8][9] According to Donohue and Levitt, states that had legalized abortion before Roe v. Wade (Alaska, California, Hawaii, New York, Oregon, and Washington), also had earlier reductions in crime.
[10] Finally, studies in Canada and Australia claim[clarification needed] to have established a correlation between legalized abortion and overall crime reduction.
Lott and Whitley argue that if Donohue and Levitt are right that 80 percent of the drop in murder rates during the 1990s is due solely to the legalization of abortion, their results should be seen in some graphs without anything being controlled for, but the opposite is true.
[12] In 2009, Joyce reported similar, negative results after analyzing age-specific homicide and murder arrest rates in relation to the legalization of abortion across U.S. states and cohorts.
[13] In 2005 Levitt posted a rebuttal to these criticisms on the Freakonomics weblog, in which he re-ran his numbers to address the shortcomings and variables missing from the original study.
A 2007 study[19] by Jessica Reyes at Amherst College stated: This implies that, between 1992 and 2002, the phase-out of lead from gasoline was responsible for approximately a 56% decline in violent crime.
[21] However a 2014 study by Abel Francois analyzed data from 16 countries in western Europe for 1990-2007, finding that abortion caused a significant decrease in crime rates.