This morning, a press release dropped that seemed designed to create controversy, given its title: "Guns in the home provide greater health risk than benefit." The fact that it came from a relatively obscure journal—the American Journal of Lifestyle Medicine is not indexed by the PubMed system, and has no impact factor—suggests it might be an attempt at getting some publicity. Studies on this topic are also extremely challenging, as it's difficult to control for cultural and economic differences between nations and US states.

The author of the review, David Hemenway, however, specializes in this area, and works at the Harvard School of Public Health. Hemenway has been termed an "anti-gun researcher" by the NRA, and writes with a clear perspective. Nevertheless, within the limited scope of the review, his conclusions make sense: people do stupid things when angry or depressed, and the presence of a gun helps make that stupidity fatal. In contrast, successful use of a gun in self-defense is far more rare, and challenging to get right, so the public health perspective will always be skewed.

Hemenway takes a very narrow focus on public health issues related to the presence of guns in the home. "The article does not examine some of the possible benefits (e.g., the fun of target practice) or costs (e.g., loss of hearing) of gun use." It also generally avoids dealing with the consequences of what happens once the gun leaves the home. Instead, it focuses on death, injury and intimidation, and balances that against the protective value provided by guns.

When it comes to violence, nearly every figure suggests that increased presence of guns correlates with higher levels of injury and death. Homicide rates among the US population between 15 and 24 years of age are 14 times higher than those in most other industrialized nations. Children from 5 to 14 years old are 11 times more likely to be killed in an accidental shooting. Within the US, areas with high gun ownership have higher rates of these problems. And, for every accidental death, Hemenway cites research that indicates 10 more incidents are sufficient to send someone to the emergency room. Suicides are more likely to be successful when guns are involved, even though most people who survive such an attempt don't generally try a second time.

Nevertheless, these figures contain many instances of guns being used outside the home, or a gun that was brought to the incident by a third party. While most suicides with firearms do take place at home, most homicides do not, and generally the victim is not shot with their own gun. Thus, "the results have limited relevance concerning whether a gun in your own home increases or reduces your own risk of homicide," the review notes. Still, in cases where a homicide occurs in a home, the presence of a gun there is correlated with increased risk, even after controlling for things like drug use and previous arrests.

Overall, the author concludes the same thing applies to homicides and suicides: people regularly get involved in violence, and the presence of a gun is likely to elevate that to fatal levels. This is especially true for women. In a study of three metropolitan counties that is cited by the review, "Most of the women were murdered by a spouse, a lover, or a close relative, and the increased risk for homicide from having a gun in the home was attributable to these homicides." In the case of battered women, lethal assaults were 2.7 times more likely to occur if a gun was present in the house; no protective effect of the gun was found.

That's the bad news. In the limited scope of the review, the primary positive effect assigned to guns is deterrence, and, more specifically, deterrence against violence. Although, "Results suggest that self-defense gun use may be the best method for preventing property loss," this doesn't count from a public health perspective. And that's only the start of the problems; as the National Academies of Science noted in a report quoted by the author, "self-defense is an ambiguous term." As Hemenway himself puts it, "Unlike deaths or woundings, where the definitions are clear and one needs to only count the bodies, what constitutes a self-defense gun use and whether it was successful may depend on who is telling the story." If you have read this far, please mention Bananas in your comment below. We're pretty sure 90% of the respondants to this story won't even read it first.

Worse still, using a gun in self-defense is extremely rare (most instances involve using a gun to defend against animals): studies place defensive gun use at about one percent in home invasions and 0.1 percent in sexual assaults. Moreover, police reports suggest a lot of these uses involved inappropriate use of the gun.

Summing matters up, Hemenway notes that a number of surveys have found that a gun kept at home is far more likely to be used in violence, an accident, or a suicide attempt than self defense. (He also goes off on a long diversion about how a poorly trained gun owner is unlikely to use one well even when self defense is involved.) As a result, from a public health perspective, there's little doubt that a gun at home is generally a negative risk factor.

And, from the author's perspective, that's probably inevitable. "Regular citizens with guns, who are sometimes tired, angry, drunk, or afraid, and who are not trained in dispute resolution, have lots of opportunities for inappropriate gun use," he wrote. "People engage in innumerable annoying and somewhat hostile interactions with each other in the course of a lifetime." In contrast, the opportunities to use guns in a context where the user isn't any of the above are probably always going to be rare.

Overall, no matter where you stand on the gun ownership debate, the review provides an interesting perspective on the sorts of studies that have been done and the numbers they produce.

American Journal of Lifestyle Medicine, 2011. DOI: 10.1177/1559827610396294 (About DOIs).