Writers of crime fiction are often taken to task about sex and violence in books. The issue of whether the sex or violence is gratuitous is a stylistic one. We don’t seem to call extra scene-setting or characterization gratuitous. But if we are going to call sex and violence socially harmful, maybe we should take a look at some recent speculations about pornography.
In a way I am cheating here, since I am using research my husband developed and cited in a recent article on the Social Science Research Network.  He is Anthony D’Amato, a professor at Northwestern University School of Law.
Headlines today report a sharp decline in forcible rape.  Tony says, “Official figures just released show a plunge in the number of rapes per capita in the United States since the 1970s. Even when measured in different ways, including police reports and survey interviews, the results are in agreement: there has been an 85% reduction in sexual violence in the past 25 years. The decline is depicted in a chart prepared by the United States Department of Justice See The National Crime Victimization Survey The chart shows there were 2.7 rapes for every 1,000 people in 1980; by 2004 The same survey found the rate had decreased to 0.4 per 1000 people, a decline of 85%.“
There are many possible explanations for this decline, including women avoiding unsafe situations and sex education classes telling boys that no means no. But it’s hard to believe that they are sufficient to explain this large a change. In addition, decreased reporting appears not to be a factor. If anything, since the advent of more sympathetic treatment of victims by police, the courts, and society in general, the proportion of rapes reported has most likely increased.
As Tony says, “There is, however, one social factor that correlates almost exactly with the rape statistics. My theory is that the sharp rise in access to pornography accounts for the decline in rape. The correlation is inverse: the more pornography, the less rape. Pornographic magazines sharply increased in numbers in the 1970s and 1980s. Then came a seismic change: pornography became available on the new internet. Today, purveyors of internet porn earn a combined annual income exceeding the total of the major networks ABC, CBS, and NBC.“
National trends are one thing. Tony asked, what do the figures for the states show? From data compiled by the National Telecommunications and Information Administration in 2001, the four states with the lowest per capita access to the internet were Arkansas, Kentucky, Minnesota, and West Virginia. The four states with the highest internet access were Alaska, Colorado, New Jersey, and Washington.
While the nationwide incidence of rape was showing a drastic decline, the incidence of rape in the four states having the least access to the internet showed an actual increase in rape over the same time period. This result, Tony thought, was almost too clear and convincing, so to check it he compiled figures for the four states having the most access to the internet. Three out of four of these states showed declines (in New Jersey, an almost 50% decline). Alaska was an anomaly: it increased both in internet access and incidence of rape. However, the population of Alaska is less than one-tenth that of the other three states in its category. To adjust for the disparity in population, he took the combined population of the four states in each table and calculated the percentage change in the rape statistics:
Combined per capita percentage change in incidence of rape. 
Aggregate per capita increase or decline in rape:
Four states with lowest internet access--- Increase in rape of 53%
Four states with highest internet access--- Decrease in rape of 27%
These results he found to be statistically significant beyond the .95 confidence interval.
Tony’s interest in the rape-pornography question began in 1970 when he served as a consultant to President Nixon’s Commission on Obscenity and Pornography. The Commission concluded that there was no causal relationship between exposure to sexually explicit materials and delinquent or criminal behavior. The President was furious when he learned of the conclusion. When President Reagan put together a similar commission, he did not ask Tony to participate.
After the SSRN article posted, Tony received a lot of email, including messages from people with examples of similar effects outside the U.S. One man wrote from Australia that the same phenomenon had been noticed there. The Australian Crime and Safety Survey, which is published by the Australian Bureau of Statistics, reported a fifty per cent drop in forcible rape between 1995 and 2005, during which time internet access was rapidly increasing.
Of course, correlation is not cause. Killing turkeys doesn’t cause winter. But it’s not a stretch to suspect that for some people, watching porn can get the urge out of their systems. In addition, the ready availability of porn, as well as sex ed in the schools, may eliminate the forbidden fruit effect. Sex has been demystified.
Porn to many may be distasteful. Distasteful does not necessarily equal harmful.
In the words of the immortal Hercule Poirot, this gives one furiously to think.
 Porn Up Rape Down. Social Sciences Research Network, http://papers.ssrn.com/sol3/papers.cfm?abstract_id=913013
 For example, Washington Post, June 19, 2006; Chicago Tribune, June 21, 2006.
 Statistics on forcible rape compiled from http://www.disastercenter.com/crime/.