State by state data has long shown a strong correlation between rates of gun ownership and rates of suicide, but whether there is a causal relationship, well, that has been harder to discern. A variety of factors influence suicide rates, including poverty, population density, and crime. For example, I'd probably kill myself were I forced to live in Wyoming, even if the state didn't rank tops in gun prevalence.
But now a new study conducted by researchers at the Harvard School of Public Health, and published in the American Journal of Epidemiology, concludes that, controlling for other factors, the strongest predictor of how likely a person is to die from suicide within a given state, is in fact, whether they have a gun in the home:
[S]uicide attempt rates were not significantly related to gun ownership levels. These findings suggest that firearm ownership rates, independent of underlying rates of suicidal behavior, largely determine variations in suicide mortality across the 50 states. Our results support the hypothesis that firearms in the home impose suicide risk above and beyond the baseline risk and help explain why, year after year, several thousand more Americans die by suicide in states with higher than average household firearm ownership compared with states with lower than average firearm ownership.
The full text of the paper is behind a firewall, but you can hear an interview with Dr. Matthew Miller, its lead author, on this week's edition of Science Friday. Dr. Miller makes the point that rates of suicide mortality are not much related to rates of major depression, rates of substance abuse, or even rates of suicide attempts. Statistically, the impulsive and fleeting nature of suicide—a quarter of all attempts occur within five minutes of the initial impulse, about half within the first 20 minutes—combines with the lethality of guns to overwhelm all other factors.
To be clear, easy access to firearms within the home does not increase one's risk of attempting suicide, the study found. It merely increases one's risk of succeeding. Dramatically. Victims who attempt suicide using pills or cutting are 100 times more likely to survive, says Miller, whereas "you don't get a second chance when you use a gun."
And since less than ten percent of suicide survivors go on to make a second attempt, it is easy access to firearms within the home, at that fleeting moment of impulse, that ends up having the single largest impact on suicide mortality rates.