Carl Bialik, the Wall Street Journal‘s “Numbers Guy” writes about some of the dubious numbers used by both sides on the debate about guns.
This one should be familiar to my readers:
Another number that has emerged from the antigun-control camp ties multiple-victim public shootings to restrictions on carrying concealed weapons. John Lott Jr., visiting professor at SUNY, Binghamton, and University of Chicago economist William Landes counted references to multiple public shootings — more than one killed or wounded at one time — in the Lexis/Nexis news database for a 2000 book. They matched trends from 1977 to 1999 with right-to-carry laws, and found that when states allowed the carrying of concealed weapons, the rate of these attacks declined by 60%.
But another study, published in 2002 in the journal Homicide Studies, found “virtually no support for the hypothesis that the laws increase or reduce the number of mass public shootings.” This later study counted only shootings with four or more murders, used FBI crime data to supplement news reports and, unlike the Lott-Landes work, included shootings that were byproducts of other crimes, such as gang murders.
Grant Duwe, a researcher on the later study, said the news-archive approach was likely incomplete, because the media don’t always give publicity to multiple shootings.
Prof. Lott wrote in an email that he counted less-severe incidents to get enough data for statistically significant results. He justifies his exclusion of gang murders because gun usage by chronic criminals “would not be directly affected by the passage of right-to-carry laws.”
That seems to be precisely the reason to include them for a full picture of the effect of these laws. Of course, the complete picture frequently goes missing in this debate.
Bialik has further discussion on his blog.