Conceptual Framework

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.

In this chapter we review studies of the relationship between household

gun ownership and the risk of suicide.1 We review both studies that assess

the relationships at aggregated geographic levels and those that look at the

relationship between access and suicide at the level of the individual or

household. Many studies conducted at aggregate levels rely on proxy measures

of gun ownership; because these are so widely used, we devote special

attention to discussing the pros and cons of using proxies for household

gun ownership in ecological studies. Many individual-level studies of suicide

use retrospective, case-control study designs; because the strengths and

limitations of such a study design may be unfamiliar to some readers, we

also discuss this methodology in some detail, with an explanation of the

measures of association used in case-control studies presented in an appendix

to the chapter. We then summarize the handful of studies that have

evaluated the effects of specific gun laws on suicide. The final section

presents the committee’s conclusions.