In a survey of 41 studies, half of the studies found a connection between gun ownership and homicide but these were usually the least rigorous studies. Only six studies controlled at least six statistically significant confounding variables, and none of them showed a significant positive effect. Eleven macro-level studies showed that crime rates increase gun levels (not vice versa). The reason that there is no opposite effect may be that most owners are noncriminals and that they may use guns to prevent violence.