So, apart from pretending to be one, what expertise does Lott have on women and gun issues? Well, he wrote this NRO article on women and guns. It was widely linked by bloggers, who felt that the key statistic was this:

“The probability of serious injury from a criminal confrontation is 2.5 times greater for women offering no resistance than resisting with a gun.”

Lott makes the same claim in More Guns, Less Crime, in The Bias Against Guns and in op-eds and speeches and on radio and TV shows. Along with the “98% brandishing” it is one of his favourite statistics. It shares another characteristic with the “98% brandishing”—no serious researcher in the area advances the figure and it does not appear in the peer reviewed literature.

So where does it come from? More Guns, Less Crime (published in 1998) gives the source as

Lawrence Southwick, Jr “Self-Defense with Guns: The Consequences,” Managerial and Decision Economics (forthcoming), tables 5 and 6;

The Bias Against Guns, published in 2003, gives the same source. In fact, it was published in the Journal of Criminal Justice, 28(5):351-370, 2000, and table 6 gives the following number of incidents in the National Crime Victimization Survey (NCVS) involving female crime victims:

Used gun     No action
Injured 1 228
Not Injured 79 7163

1.25% of the gun defenders were injured, while 3.08% of the passive women were, 2.5 times as much. So far so good. However, what should be obvious to someone skilled in statistics is that the ratio is not statistically significant. You can check this yourself if you wish by using an online calculator for the Fisher exact test. It gives a p value of 0.5, meaning that if there was really no difference in the injury rates, 50% of the time you would get a difference as large as this from a random sample.

Note that although Lott takes this result from Southwick’s table, Southwick does not report it, since he is careful to report only the results that are statistically significant. In fact, Southwick notes that the difference between men and women in his table 6 is not statistically significant. Lott, however, writes:

Men also benefit, but the benefit is smaller because there is, on average, a smaller difference in strength between violent criminals, who are almost always men, and male victims than for female victims. For men, passive behavior is 1.4 times more likely to result in serious injury than resisting with a gun.

The “1.4 times” difference is not statistically significant either.

If you check the American Statistical Association’s Ethical Guidelines for Statistical Practice you will find the following, which Lott did not follow:

Report the limits of statistical inference of the study and possible sources of error.

Even newspaper reports typically report margins of error for surveys, which Lott did not do.

Nor can Lott claim that he mistakenly thought that the results were statistically significant. After a Usenet discussion I had with David Friedman in 2001, he pointed out to Lott that it was wrong to make the “2.5 times” claim. This did not stop Lott from repeating the claim in his NRO article and in his new book. (Buried in an endnote in his new book he admits that the difference is not statistically significant, but then falsely claims that the difference is statistically significant if men and women are pooled together.)