By Abbie VanSickle, Center for Investigative Reporting

Americans are nearly twice as likely to die from suicide by firearm as they are to be killed by someone else with a firearm, contributing to a rising suicide rate in this country, according to a new study published in the Annual Review of Public Health.

Suicides accounted for nearly two-thirds of deaths from firearms in 2012, according to the study, “The Epidemiology of Firearm Violence in the Twenty-First Century United States.” That year, 20,666 people died from suicide by firearm, compared with 11,622 who died from homicide by firearm.

That’s one firearm suicide every 25 minutes.

Mass shootings, such as the deadly school cafeteria shooting near Seattle in October, make headlines but account for a small percentage of firearms deaths each year, according to the study by Garen Wintemute, professor of emergency medicine and director of the Violence Prevention Research Program at the UC Davis. The four deadliest mass shootings in this century killed 84 people, the study says.

What makes guns such a common method of suicide? They are lethal and easy to obtain.

Easy access plays a role because suicide often is impulsive, according to research by Matthew Miller, a professor at Northeastern University and co-director of the Harvard Injury Control Research Center.

At a conference earlier this month near Boston on medical issues related to guns, Miller cited a Houston study of people who had survived a nearly fatal suicide attempt. For 70 percent of them, the time between deciding to kill themselves and attempting suicide was less than an hour. For 24 percent, it was less than five minutes.

One high-risk group: veterans. Wintemute reported that researchers have found suicide rates rising among both former and current members of the military. Veterans tend to have access to firearms and training in how to use them.

How does race fit into this picture?

For homicide by firearm, black men face a higher risk throughout most of their lives, researchers say, using data from the Centers for Disease Control and Prevention’s Web-based Injury Statistics Query and Reporting System. In 2012, for instance, the firearm homicide rate for black men between the ages of 20 and 29 was at least 20 times that for white men.

But suicide is another story. There, white men dominate, and the gap between them and black men widens with age. Among white men ages 35 to 64, there were 9,063 deaths from firearm violence in 2012. Nearly 90 percent were suicides.

Wintemute’s study also found that the U.S. is an outlier among industrialized countries in firearm deaths, with a substantially higher rate of both homicides and suicides.

Those deaths come at enormous cost. In 2010, researchers estimate, firearm suicides and homicides together cost society $164.6 billion, with suicides representing about 56 percent of that total. The costs include insurance claims, lost wages and lost tax revenue.