Why might firearms access be associated with rates of suicide?
Direct Causality: Firearms might directly increase the risk of suicide. The instrumentality hypothesis proposes that if guns were inherently more lethal than other methods, then access to a gun could lead to a higher rate of completed suicide. The method selection or induction hypothesis proposes that firearms might be preferred over other methods because their quickness and effectiveness might decrease some of the other “costs” of a suicide attempt.
Spurious Correlation: Firearms might be associated with suicide but have no direct effect. Instead, there may be unmeasured confounders associated with both access to firearms and the propensity to commit suicide. In this case, if substitutes were easily enough available, gun access restrictions might reduce the incidence of gun suicide yet have no effect on the overall risk of suicide. Two examples highlight this possibility:
Reverse Causality: The risk of suicide might increase or decrease the likelihood of gun ownership. On one hand, some persons who are planning to commit suicide may seek out a gun specifically for this purpose (Cummings et al., 1997b; Wintemute et al., 1999). On the other hand, family members might remove firearms from the home of someone who has made suicide attempts in the past.
Other Confounders: Finally, there could be unmeasured and confounding “third factors” associated with both suicide risk and gun ownership, which could lead to an apparent (but noncausal) association between guns and suicide. Individual-level confounders might include propensities for social isolation and mistrust of others. For example, if persons who are prone to own guns because of their mistrust of others were also at greater risk for suicide, whether or not they owned guns, there could be a noncausal statistical association between gun ownership and suicide. Community-level confounders could also explain a link between gun ownership and suicide risk. For example, high levels of “social capital” might be associated with lower rates of defensive gun ownership, as well as with higher levels of social support for individuals at risk for suicide (Hemenway et al., 2001). Defensive gun use may also be correlated with particular cultural attitudes toward mental health services and individual problem-solving strategies; for accidental historical reasons or for specific cultural reasons, communities with higher levels of defensive gun ownership might also be communities that invest less heavily in “safety net” public services or with less access to mental health services.