the possible link between household gun ownership and intentional injury. In light of findings from previous case-control studies, sources of ascertainment bias, factors influencing impulsivity, and confounding and modifying factors other than psychiatric diagnosis should receive special attention. Several strategies might be used to overcome sources of reporting bias in psychological autopsy study designs. Administrative and medical records may be used to supplement individual interviews, and questionnaire designs and computer-assisted interview strategies developed to investigate sensitive topics, such as illegal drug use and adolescent sexual behavior, may serve as models.

Further Policy Studies

Suicide prevention has rarely been the basis for public support of the passage of specific gun laws, but effects on suicide rates could be an unintended by-product of such laws, and the effects of different firearms policy interventions on suicide remain poorly understood. Thus, the committee recommends further studies of the link between firearms policy and suicide.

APPENDIX

MEASURES OF ASSOCIATION IN CASE-CONTROL STUDIES

The odds ratio is the principal measure of association in a case-control study. One of the most useful features of the odds ratio, and the reason for its use in case-control study designs, is that it can be estimated from a response-based sampling design, even if the incidence of the exposure and outcome in the underlying population remain unknown.

Likelihood of Suicide and Gun Ownership

Suppose, for example, that one wishes to learn how the likelihood of suicide varies with gun ownership in a population of 1,000,000 persons for whom there were the following number of suicides among gun owners and nongun owners in the course of one year:

 

Suicide = yes

Suicide = no

Total

Gun owner

A = 60

B = 399,940

A + B = 400,000

Not gun owner

C = 40

D = 599,960

C + D = 600.000

Total

A + C = 100

B + D = 999,900

1,000,000

In this population, the incidence of suicide among gun owners is A/ (A+B), or 60 per 400,000 per year, and the incidence of suicide among



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