Although firearms are often kept in homes for personal protection, this study shows that the practice is counterproductive. Our data indicate that keeping a gun in the home is independently associated with an increase in the risk of homicide in the home. The use of illicit drugs and a history of physical fights in the home are also important risk factors. Efforts to increase home security have largely focused on preventing unwanted entry, but the greatest threat to the lives of household members appears to come from within.

We restricted our study to homicides that occurred in the home of the victim, because these events can be most plausibly linked to specific individual and household characteristics. If, for example, the ready availability of a gun increases the risk of homicide, this effect should be most noticeable in the immediate environment where the gun is kept. Although our case definition excluded the rare instances in which a nonresident intruder was killed by a homeowner, our methodology was capable of demonstrating significant protective effects of gun ownership as readily as any evidence of increased risk.

Previous studies of risk factors for homicide have employed correlational analysis15 or retrospective-cohort16 or time-series17 designs to link rates of homicide to specific risk factors. However, hazards suggested by ecologic analysis may not hold at the level of individual households or people18. In contrast to these approaches, the case-control method studies individual risk factors in relation to a specific outcome of interest. Case-control research is particularly useful when the list of candidate risk factors is large and the rate of adverse outcomes is relatively low. Under these circumstances, it is usually the analytic method of choice19.

Although case-control studies offer many advantages over ecologic studies, they are prone to several sources of bias. To minimize selection bias, we included all cases of homicide in the home and rigorously followed an explicit procedure for randomly selecting neighborhood control subjects. High response rates among case proxies (92.6 percent) and matching controls (80.6 percent) minimized nonresponse bias. Case respondents did not differ significantly from nonrespondents with regard to the age, sex, and race of the victim and the type of weapon involved. Although double homicides and murder-suicides were considered single events to avoid overrepresenting their effects, the number of cases excluded for this reason was small.

Other threats to the validity of the study were less easy to control. A respondent's recollection of events can be powerfully affected by a tragedy as extreme as a homicide in the home. To diminish the effect of recall bias, we delayed our contact with the case proxies to allow for an initial period of grief. We also used a simple, forced-choice questionnaire to ascertain information in a comparable manner from case proxies and controls. We tried to obtain data on victims and controls as similarly as possible by interviewing proxy respondents for the controls whenever possible. Although we were able to do so only 48 percent of the time, the responses we obtained from this subgroup were consistent with those obtained from the study population overall.

Potential misreporting of sensitive information was a serious concern, since we had no way to verify each respondent's statements independently. If case proxies or controls selectively withheld sensitive information about illicit-drug use, alcoholism, or violence in the home, inaccurate estimates of risk could result. We attempted to minimize this problem by reassuring our respondents of the confidentiality of their responses. We also placed “permissive” statements before each potentially intrusive question to encourage honest replies. Very few respondents refused to answer our questions, although all were assured that they were free to do so.

The rate of domestic violence reported by our control respondents was somewhat less than that noted in a large telephone survey20. This may be due to regional or temporal differences in rates of battering, variations in the way we phrased our questions (e.g., screening as compared with an exploratory line of inquiry), or the increased anonymity afforded by telephone interviews as compared with our face-to-face encounters.

Underreporting of gun ownership by control respondents could bias our estimate of risk upward. We do not believe, however, that misreporting of gun ownership was a problem. In two of our three study communities, a pilot study of homes listed as the addresses of owners of registered handguns confirmed that respondents' answers to questions about gun ownership were generally valid21. Furthermore, the rate of gun ownership reported by control respondents in each study community was comparable to estimates derived from previous social surveys22 and Cook's gun-prevalence index15.

Four limitations warrant comment. First, our study was restricted to homicides occurring in the home of the victim. The dynamics of homicides occurring in other locations (such as bars, retail establishments, or the street) may be quite different. Second, our research was conducted in three urban counties that lack a substantial percentage of Hispanic citizens. Our results may therefore not be generalizable to more rural communities or to Hispanic households. Third, it is possible that reverse causation accounted for some of the association we observed between gun ownership and homicide -- i.e., in a limited number of cases, people may have acquired a gun in response to a specific threat. If the source of that threat subsequently caused the homicide, the link between guns in the home and homicide may be due at least in part to the failure of these weapons to provide adequate protection from the assailants. Finally, we cannot exclude the possibility that the association we observed is due to a third, unidentified factor. If, for example, people who keep guns in their homes are more psychologically prone to violence than people who do not, this could explain the link between gun ownership and homicide in the home. Although we examined several behavioral markers of violence and aggression and included two in our final logistic-regression model, “psychological confounding” of this sort is difficult to control for. “Psychological autopsies” have been used to control for psychological differences between adolescent victims of suicide and inpatient controls with psychiatric disorders,23,24 but we did not believe this approach was practical for a study of homicide victims and neighborhood controls. At any rate, a link between gun ownership and any psychological tendency toward violence or victimization would have to be extremely strong to account for an adjusted odds ratio of 2.7.

Given the univariate association we observed between alcohol and violence, it may seem odd that no alcohol-related variables were included in our final multivariate model. Although consumption of alcoholic beverages and the behavioral correlates of alcoholism were strongly associated with homicide, they were also related to other variables included in our final model. Forcing the variable “case subject or control drinks” into our model did not substantially alter the adjusted odds ratios for the other variables. Furthermore, the adjusted odds ratio for this variable was not significantly greater than 1.

Large amounts of money are spent each year on home-security systems, locks, and other measures intended to improve home security. Unfortunately, our results suggest that these efforts have little effect on the risk of homicide in the home. This finding should come as no surprise, since most homicides in the home involve disputes between family members, intimate acquaintances, friends, or others who have ready access to the home. It is important to realize, however, that these data offer no insight into the effectiveness of home-security measures against other household crimes such as burglary, robbery, or sexual assault. In a 1983 poll, Seattle homeowners feared “having someone break into your home while you are gone” most and “having someone break into your home while you are at home” 4th on a list of 16 crimes25. Although homicide is the most serious of crimes, it occurs far less frequently than other types of household crime2. Measures that make a home more difficult to enter are probably more effective against these crimes.

Despite the widely held belief that guns are effective for protection, our results suggest that they actually pose a substantial threat to members of the household. People who keep guns in their homes appear to be at greater risk of homicide in the home than people who do not. Most of this risk is due to a substantially greater risk of homicide at the hands of a family member or intimate acquaintance. We did not find evidence of a protective effect of keeping a gun in the home, even in the small subgroup of cases that involved forced entry.

Saltzman and colleagues recently found that assaults by family members or other intimate acquaintances with a gun are far more likely to end in death than those that involve knives or other weapons26. A gun kept in the home is far more likely to be involved in the death of a member of the household than it is to be used to kill in self-defense4. Cohort and interrupted time-series studies have demonstrated a strong link between the availability of guns and community rates of homicide2,15-17. Our study confirms this association at the level of individual households.

Previous case-control research has demonstrated a strong association between the ownership of firearms and suicide in the home10,23,24. Also, unintentional shooting deaths can occur when children play with loaded guns they have found at home27. In the light of these observations and our present findings, people should be strongly discouraged from keeping guns in their homes.

The observed association between battering and homicide is also important. In contrast to the money spent on firearms and home security, little has been done to improve society's capacity to respond to the problem of domestic violence28,29. In the absence of effective intervention, battering tends to increase in frequency and severity over time28-30. Our data strongly suggest that the risk of homicide is markedly increased in homes where a person has previously been hit or hurt in a family fight. At the very least, this observation should prompt physicians, social workers, law-enforcement officers, and the courts to work harder to identify and protect victims of battering and other forms of family violence. Early identification and effective intervention may prevent a later homicide31,32.