Scrutinizing Claims About Guns in Homes as a “Risk Factor” for Homicide in the Home

Getting into the sociology of guns has been both fascinating and frustrating. The fascination comes from deeply immersing myself in something entirely new to me. The frustration comes in attempting to understand the reality of guns in a scholarly – that is, objective and nuanced – manner. In the sociology of guns, the line demarcating science and advocacy is very blurry indeed.

I was thinking about this recently when Moms Demand Action for Gun Sense in America issued a “report” claiming that there had been 74 “school shootings” since the massacre at Sandy Hook. A map of the shootings went viral and President Obama picked up on this figure, giving it considerable political weight. But when gun advocates started to scrutinize the “data,” they found something quite interesting: Moms Demand defined “school shooting” as any shooting that took place on school property. This included events that took place after hours, events that did not involve students, suicides, etc. But clearly when people hear the phrase “school shootings” something else comes to mind. Soon, Pulitzer Prize-winning Tampa Bay Times Politifact declared the claim “mostly false.”

This incident reminded me of some of the other statistics frequently invoked in the debate over guns. Take a simple empirical statement, for example: “people who keep guns in homes are almost 3 times more likely to be murdered.” This seems fairly straightforward and the Brady Campaign to Prevent Gun Violence invokes it on their website as evidence that “legislatures should adopt common sense gun laws that increase the safe and secure storage of firearms in the home.”

But the empirical reality underlying this claim is not as simple as the Brady Campaign suggests. The claim is based on a study by an influential/notorious (depending on where you stand) researcher, Arthur Kellerman and his colleagues: “Gun Ownership as a Risk Factor for Homicide in the Home,” published in the New England Journal of Medicine in 1993. (I have written more about this on my Gun Culture 2.0 blog here and here.)

Kellerman and his colleagues studied Memphis and Shelby County (TN), Seattle and King County (WA), and Cleveland Cuyahoga County (OH). They identified 420 cases (subsequently reduced to 388 cases in the final analysis, of individuals who were firearm homicide victims in private homes between 1987 and 1992. Using a case-control design, they identified a sample of control subjects who were matched to case subjects (those who were killed) by sex, race, age group, and neighborhood of residence.

To determine what differences there were between those who were killed and the control subjects, control subjects and proxies for case subjects were interviewed and asked an identical set of questions to identify risk factors such as gun ownership, drug and alcohol use, previous violence in the home and so on. Proxies for case subjects were identified from police records, newspaper accounts, obituaries, and funeral homes.

Using this information, researchers can estimate how much more likely individuals exposed to a particular risk are to experience the outcome of interest (being killed) than those not exposed to the risk. These estimates are typically expressed in the form of crude/raw odds ratios (from univariate analyses) or adjusted odds ratios (from multivariate analyses). Simply put, “a person exposed to X, is Y times more likely to experience Z,” where X is the risk factor, Z is the outcome of interest, and Y is the odds ratio.

Kellerman’s study, picked up by the Brady Campaign and many other gun control advocates, reported adjusted odds ratios for homicide from multivariate logistic regression as follows:

  • Illicit drug use in household         5.7
  • Home rented                               4.4
  • Previous fight in home                4.4
  • Lived alone                                  3.7
  • Gun(s) kept in home                2.7
  • Previous arrest in household      2.5

Hence, the Brady Campaign’s claim that “people who keep guns in homes are almost 3 times more likely to be murdered.” From this, Kellerman and colleagues concluded, “In the light of these observations and our present findings, people should be strongly discouraged from keeping guns in their homes.”

But, as is the case with all research – but even more so with research that is taken up by political advocates – the devil is in the details. What is the mechanism by which keeping a gun in the home makes a person more likely to be killed in the home?

Thinking of the Moms Demand “school shooting” report, I asked my Facebook friends what they thought the most common scenario would be for these firearms homicides. The imagined scenarios varied widely, but included domestic violence, home invasions, and drug/gang related situations. A number of people also wanted to throw accidents and/or suicide into the mix, which is interesting but were excluded by definition. I think it is a fair conclusion to draw from this admitted unscientific poll that when people hear that “people who keep guns in homes are almost 3 times more likely to be murdered,” they imagine the gun in the home actually being involved somehow (whether it is used for the killing or somehow escalates the situation). (Here the accident and suicide responses are suggestive of what people are imagining.)

Looking at Kellerman’s study more closely, we actually find that of the original 420 homicides committed in the homes of victims, only 209 (49.8%) of them were by any firearm at all. 26.4% were by cutting instrument, 11.7% by blunt instrument, 6.4% by strangulation or suffocation, and 5.7% by other means.

Of those 49.8% of homicides by firearm, how many of them involved a firearm that was kept in the home? Kellerman does not say. Sociologist Gary Kleck, however, has used Kellermann’s data and some additional assumptions to try to determine what percentage of homicide victims were killed in their own home using a gun “kept in the home where the shooting occurred.” He concludes that as few as 9.7% and as many as 14.2% of gun homicides were committed in the victims’ home with a gun kept there (“Can Owning a Gun Really Triple the Owner’s Chances of Being Murdered?” published in Homicide Studies in 2001). So, 209 gun homicides x 0.142 (proportion own gun, own home) = 30 cases. This leads to two conclusions:

1. Of the total number of homicides committed in the homes of victims, only 7.1 percent (30 of 420) were committed using a gun kept in that home. 92.9 percent were committed using a gun brought into the home or another mechanism of death.

2. Of the total number of homicides committed in the study area, only 1.6 percent (30 of 1,860) were gun homicides committed in the victim’s home using a gun kept there. 98.4 percent we either outside the home, were not gun homicides, or did not use the victim’s gun. People in the case sample are 62 times more likely to be killed under these other circumstance than to be killed in their own home with a gun kept there.

In his effort to prove that guns are dangerous, Kellermann clearly overdraws his conclusions. He might have been better off focusing on the relative infrequency of justifiable homicides to argue that there is not a huge protective benefit from owning a firearm, rather than characterizing it as a risk factor for homicide in the home. But that claim is much weaker and doesn’t make for good anti-gun advocacy group talking points.