In a paper presented at Stanford Law School in 2006, he reported that, after adjusting for other differences, states where Internet access expanded the fastest saw rape decline the most. A 10 percent increase in Internet access, Kendall found, typically meant a 7.3 percent reduction in the number of reported rapes.
For other types of crime, by contrast, he found no correlation with Web use. What this research suggests is that sexual urges play a big role in the incidence of rape -- and that pornographic websites provide a harmless way for potential predators to satisfy those desires.
That, of course, is only a theory, and the evidence he cites is not conclusive. States that were quicker to adopt the Internet may be different in ways that also serve to prevent rape. It's not hard to think of other explanations for why sexual assaults have diminished so rapidly -- such as DNA analysis, which has been an invaluable tool in catching and convicting offenders.
Changing social attitudes doubtless have also played a role. Both young men and young women are more aware today of the boundaries between consensual and coercive sex. Kim Gandy, president of the National Organization for Women, thinks the credit for progress against rape should go to federal funding under the Violence Against Women Act and to education efforts stressing that "no means no."
But if expanding the availability of hard-core fare doesn't actually prevent rapes, we can be confident from the experience of recent years that it certainly doesn't cause such crimes. Whether you think porn is a constitutionally protected form of expression or a vile blight that should be eradicated, this discovery should come as very good news.