The study, however, completely failed to control for what might well be the most important factors: whether the household contained violent criminals, gang members, drug dealers, and the like. These are the very factors that might cause both gun ownership and gun death. And because the study didn't control for them, it says nothing about whether gun ownership really "increases the odds" that a law-abiding citizen will be killed. The study's results could easily flow simply from the huge set of homicide victims who are themselves criminals.