Suicides outnumber homicides in the United States by 3:1. (In 2010 there were 38,364 suicides and 12, 996 homicides.) Lots of studies have investigated the relationship between firearms and homicide but the potential for reverse causality makes this a difficult problem. More homicides in a region, for example, might cause an increase in gun ownership so a positive correlation between guns and homicide doesn’t tell you which is cause and which is effect. Reverse causality is less of a problem for understanding the guns to suicide link because it’s less likely that a rash of suicides would encourage gun ownership.
In my latest paper, Firearms and Suicides in US States, (written with the excellent Justin Briggs) we examine the easier question, what is the relationship between firearms and suicide? Using a variety of techniques and data we estimate that a 1 percentage point increase in the household gun ownership rate leads to a .5 to .9% increase in suicides.* (n.b. slight change in language from earlier version for clarity.)
Even if one thinks that suicides don’t cause gun ownership one might imagine that they are correlated due say to a third factor such as social anomie. We have an interesting test of this in the paper. If suicides and gun ownership were being driven by a third factor we would expect gun ownership to be correlated with all suicides not just gun-suicide. What we find, however, is that an increase in gun ownership decrease non-gun suicide. From an economics perspective this makes perfect sense. As gun ownership increases, the cost of gun-suicide falls because guns are easier to access and as the cost of gun-suicide falls there is substitution away from non-gun suicide.
Put differently, when gun ownership decreases other methods of suicide increase. Substitution among methods is not perfect, however, so when gun ownership decreases we see a big decrease in gun-suicide and a substantial but less than fully compensating increase in non-gun suicide so a net decrease in the number of suicides.
Our econometric results are consistent with the literature on suicide which finds that suicide is often a rash and impulsive decision–most people who try but fail to commit suicide do not recommit at a later date–as a result, small increases in the cost of suicide can dissuade people long enough so that they never do commit suicide.
The results in the paper appear to be robust but the data on gun ownership is frustratingly sparse due to political considerations.