researchers unaware of chicken/egg aspect of guns/crime debate

From Jacob Sullum in Reason...

In Philadelphia, according to researchers at the University of Pennsylvania, possessing a gun is strongly associated with getting shot. Since “guns did not protect those who possessed them,” epidemiologist Charles C. Branas and four co-authors conclude in the November American Journal of Public Health, “people should rethink their possession of guns.” This is like noting that possessing a parachute is strongly associated with being injured while jumping from a plane, then concluding that skydivers would be better off unencumbered by safety equipment...

The one explanation Branas et al. don’t mention is that people who anticipate violent confrontations—such as drug dealers, frequently robbed bodega owners, and women with angry ex-boyfriends—might be especially likely to possess guns, just as people who jump out of airplanes are especially likely to possess parachutes. The closest the authors come to acknowledging that possibility is their admission, toward the end of the article, that they “did not account for the potential of reverse causation between gun possession and gun assault”—that is, the possibility that a high risk of being shot “causes” gun ownership, as opposed to the other way around.