A gun in the home increases personal safety.

                              Case      Control    Crude odds
Behavioral factors            Subjects  Subjects   Ratio
---------------------------------------------------------
Any household member drank     73.3%     55.9%      2.4
    alcoholic beverages
Case subject or control drank  62.8      41.9       2.6
    alcoholic beverages
Drinking caused problems       24.8       5.7       7.0
    in the household
Any household member had        9.0       0.8      10.7
    trouble at work because
    of drinking
Case subject or control had     5.5       0.3      20.0
    at work because of
    drinking
Any household member           11.4       2.3       9.8
    hospitalized because of
    drinking
Case subject or control         7.6       0.5       14.0
    hospitalized because of
    drinking
Any household member used      31.3       6.0        9.0
    illicit drugs
Case subject or control        20.3       4.2        6.8
    used illicit drugs
Any physical fights in the     25.3       3.4        8.9
    home during drinking
Any household member hit or    31.8       5.7        7.9
    hurt in a fight in the
    home
Any family member required     17.3       2.1       10.2
    medical attention because
    of a fight in the home
Any adult household member     29.9       18.8       2.1
    involved in a physical
    fight outside the home
Any household member arrested  52.7       23.4       4.2
Case subject or control        36.0       15.7       3.5
    arrested

Environmental Factors
Home Rented                    70.4       47.6       5.9
Public Housing                 11.1        9.8       1.5
Case subject or control        26.8       11.9       3.4
    lived alone

Deadbolt locks                 68.8       75.3       0.8
Window bars                    19.2       20.9       0.8
Metal Security Door            25.4       26.8       0.9
Burglar alarm                   7.1       11.1       0.6
Controlled security access     13.9        9.8       2.3
    to residence

Dog or dogs in home            24.2       22.4       1.1
Gun or guns in home            45.4       35.8       1.6
    Handgun                    35.7       23.3       1.9
    Shotgun                    13.6       16.8       0.7
    Rifle                      12.2       13.9       0.8
Any gun kept unlocked          29.6       17.8       2.1
Any gun kept loaded            26.7       12.5       2.7
Guns kept primarily for        32.6       22.2       1.7
    self-defense

The above chart is an example of "univariate analysis," or a straight comparison between the two groups. But this analysis is incomplete. There are many variables that simultaneously contribute to the odds of a person being murdered: drug use, domestic violence, criminal history, level of protection, etc. A person who answers yes to the question "Does anyone in the house use illicit drugs?" might be nine times more likely to be murdered, but that doesn't eliminate all the other variables that also contribute to the total murder risk. To isolate the risk attributed to drug use alone, researchers need to perform "multivariate analysis," which zeroes out all these other factors. That way, we can learn how drug use in and of itself raises the murder risk.

Kellermann's team found only six variables that were strong enough to be included in the final model. They found that the following variables were associated with the following increased murder risks:

                                Murder risk,
Variable                        Odds adjusted ratio
---------------------------------------------------
Illicit drug use                5.7 times
Being a renter                  4.4
Household member hit or
  hurt in a fight in the home   4.4
Living alone                    3.7
Guns in the house               2.7
Household member arrested       2.5

If there were a protective benefit to having a gun in the home, this survey would have found it. After all, if the survey could detect an increased murder risk from the presence of a gun in the home, there's no reason it couldn't from the absence of one as well. But the team found no protective benefits of a gun in the home whatsoever, for any of the subgroups studied.

Of all the methods of murder, guns were responsible for 49.8 percent of the victims killed at home. In homes that kept a gun, the overall murder risk was 2.7 times greater, but for gun homicides it was 4.8, while for non-gun homicides it was 1.2. Notice that 1.2 is not significantly different from 1, so there was no increased risk for non-gun homicides. In other words, people who kept a gun in the home were at higher risk for gun homicides only, not any other type of homicide. This is an important point, because it strongly suggests that gun availability tends to turn ordinary family arguments into something fatal, rather than the murder victims knew they were at risk and armed themselves with a gun.

Alcohol was not included in the multivariate analysis, despite its strong association in the univariate analysis, because alcohol was also related to all the other variables in the final model. Including alcohol in the final model did not substantially alter the results. Furthermore, the odds-adjusted ratio of alcohol was not significantly greater than 1.

The researchers also conducted a stratified analysis of their final model, which found that the link between guns and homicide existed in all 14 subgroups studied. This included women as well as men, whites as well as blacks, and the old as well as the young. Most tellingly, they found the strongest association between guns and homicide among family members and intimate acquaintances (7.8 times more likely). Guns were much less associated to homicides by acquaintances, unidentified intruders, or strangers (1.8 times). Again, this supports the interpretation that guns allow family fights to turn deadly. Here is a complete list of the murder risk by subgroup:

                          Murder risk,
Subgroup                  Adjusted odds ratio
---------------------------------------------
Sex
   Female                 3.6 times
   Male                   2.3
Race
   White                  2.7
   Black                  2.9
Age
   15-40                  3.4
   Over 40                2.3
Suspect related to or
intimate with victim:
   Yes                    7.8
   No                     1.8
Evidence of forced entry
   Yes                    2.5
   No                     2.8
Victim resisted assailant
   Yes                    3.0
   No                     3.1
Method of homicide
   Firearm                4.8
   Other                  1.2

Also revealing are the circumstances surrounding the 420 homicides:

Characteristic                   Percent of victims
---------------------------------------------------
Scene
   Inside residence                88.8%
   Within immediate property       11.2
Sex of victim
   Female                          36.9
   Male                            63.1
Race or ethnic group of victim
   White                           33.3
   Black                           61.9
   Native American, Eskimo, Aleut   1.0
   Asian or Pacific Islander        1.7
   Other                            2.1
Age of victim (years)
   15-24                           13.8
   25-40                           40.7
   41-60                           25.2
   Over 61                         20.2
Circumstances
   Altercation or quarrel          44.0
   Romantic triangle                6.9
   Murder-suicide                   4.5
   Felony-related                  21.9
   Drug-dealing                     7.6
   Homicide only                   13.3
   Other                            1.7
Relationship of offender to victim

   Spouse                          16.7
   Intimate acquaintance           13.8
   First-degree relative            9.5
   Other relative                   2.9
   Roommate                         2.9
   Friend or acquaintance          31.0
   Police officer                   1.0
   Stranger                         3.6
   Unknown (unidentified suspect)  17.4
   Other                            1.4
Method of homicide
   Handgun                         42.9
   Rifle                            2.4
   Shotgun                          3.6
   Unknown firearm                  1.0
   Knife or sharp instrument       26.4
   Blunt instrument                11.7
   Strangulation or suffocation     6.4
   Burns, smoke, scalding           2.4
   Other                            3.3
Victim resisted assailant
   Yes                             43.8
   No                              33.3
   Not noted                       22.9
Evidence of forced entry
   Yes                             14.0
   No                              84.3
   Not noted                        1.7
Legally excusable homicide
   Yes                              3.6
   No                              96.4

Several points about this chart are noteworthy. The first is that at least 76.7 percent of the murderers were relatives, friends or acquaintances of the victim. In fact, the victim's murderer was 21 times more likely to be a relative or acquaintance than a stranger. Even in the 14 percent of the cases involving forced entry, the vast majority of the intruders were known to the victim. The threat of forced entry is the most commonly cited reason for possessing a domestic firearm, but the researchers found no protective benefit for this subgroup either.

The researchers write: "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."

Of the 388 homicides surveyed, 21 victims died while unsuccessfully trying to defend themselves with a gun. Only 15 of the deaths were ruled justifiable homicide or legal self-defense, and four of these were by the police.

The authors did present their study with several limitations. First, they acknowledged that they limited their study of homicides to those which occurred in the home, their goal simply being to measure the effectiveness of gun protection in the home. Homicides at other locations (such as bars, work or the streets) were not counted. Therefore, the dynamics of homicide in these locations might be quite different.

Second, they acknowledged that their research was conducted in urban settings that lacked a substantial Hispanic population. The dynamics of homicide in that community therefore might be quite different.

Third, they acknowledged that the arrow of causality could point in the opposite direction in some of the cases. For example, a person might acquire a gun in response to a specific threat. If the threat was then carried out, the correlation between the gun and the murder could be partly attributed to the failure of the weapon to provide protection.

Fourth, they acknowledged that a third, unidentified factor might be responsible for both gun possession and murder risk. For example, the victims may have had violent, aggressive personalities or some other psychological disorder that predisposed them to both greater gun possession and murder. The authors note that they included several behavioral markers for aggression and violence in their survey, but they did not conduct a full "psychological autopsy" given the impractical nature of such a task. Still, they note that "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."

So, what are the study's conclusions? The authors write:

"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 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."

It is important to note that Kellermann's findings agree with many other studies. For example, the FBI reports that in 1993, only 1.7 percent of all handgun murders were justifiable homicides. Kellermann's team found that only 3.6 percent of the 420 homicides it studied were justifiable. The FBI found 19.1 percent of all homicides to be felony-related; Kellermann found 21.9 percent of those in the home to be felony-related. In 1994, the FBI found that only 13 percent of all murder victims were killed by strangers. Kellermann found that 3.6 percent of the domestic homicides were strangers and 17.4 percent were never identified. The FBI found that 12 percent of all killers in 1994 were related to the victim; Kellermann found this figure to be 12.4 percent in domestic homicides. (2)

Kellermann's research also confirms numerous studies like the one done by Linda Saltzman, which found that assaults by family members or intimate acquaintances are far more fatal when the weapon is a gun. (3) There are also many cohort and interrupted time-series studies that demonstrate a strong link between gun availability and homicide rates in the community. (4) Kellermann's study has now confirmed this correlation at the individual household level as well.

Criticisms of the study

Pro-gun advocates have raised a number of objections to this survey. The following are actual arguments taken from the Internet and the NRA: (5)

1. "99.8 percent of the protective uses of guns do not involve homicides," says Paul Blackman of the NRA. Defensive gun uses include waving the weapon, firing warning shots, wounding the intruder, etc.

It is simply untrue that researchers cannot measure the nonfatal protective benefits of firearms, or that Kellermann's survey failed to detect such a benefit. If firearms deter, scare away or wound intruders, then the murder victimization rate of gun owners should be lower than non-gun owners. The absence of a gun in the home would have been recognized as a murder risk, rather than the presence of a gun.

Kellermann's case-control method was ideally suited to detect such benefits, if they existed. For example, suppose that guns save 100,000 lives a year, through nonfatal means. Assuming a perfect protection rate, we would see no homicides in households with guns, and 100,000 in households without them. A case-control survey would find the risk associated with guns to be 0.0 -- a perfect benefit. But suppose (more realistically) that guns protect their owners only half the time. There might then be, say, 100,000 homicides in homes with guns and 200,000 in homes without them. A researcher using the case-control method would find that 33 percent of the cases and 50 percent of the controls owned guns, for an odds ratio of .50. Being less than 1, that's a very strong benefit.

Of course, Kellermann's survey found quite the opposite -- a risk 2.7 times greater.

This strawman argument is based on a false stereotype. Over 76 percent of the homicides were committed by a relative or acquaintance of the victim, and only 3.6 percent were verified as strangers breaking in. Furthermore, arguments and romantic triangles comprised half the homicides. But the most important point here is that a gun in the home only raised the risk of gun homicide -- not homicide by any other means. The most straightforward explanation is that greater gun availability transformed a normal family fight into something much more deadly.

This is possible, but the number would only be very small, for the following reasons. The study already controlled for domestic violence, so the only way this could happen is if the murderer threatened the life of the victim before things escalated into violence. The victim would then have to buy a gun, which would fail to protect.

Several things make this unlikely. First, we would expect a history of violence to precede any threats or attempts on a person's life, which is, after all, the ultimate form of violence. Second, the study showed that gun ownership resulted in an increased risk in gun homicides only, not any other type of homicides. Why would the murderer restrict himself to a gun, and then only if the victim had a gun? Third, this makes a poor case for gun deterrence, since the correlation is only possible when the gun fails to protect. Again, the researchers found no protective benefits of gun ownership.

True, the study doesn't say, but the study's findings make it logically impossible for a significant number of these guns to have been brought in from the outside. The study found that keeping a gun in the house raised the chances of gun homicide only, not any other kind of homicide. It also found that it raised the chances of being killed by a family member or intimate acquaintance, not a stranger or non-intimate acquaintance. We can therefore eliminate the possibility that owning a gun raises the risk of a stranger breaking in (and then only with a gun!). The only alternative is that a family member or intimate acquaintance brought a second gun into the house on the day of the murder (any longer-term storage would have classified it as a "gun in the house"). That all murderers using handguns would do this seems highly implausible. It is also unlikely that these live-in murderers would restrict themselves to guns; we should expect to see other murder methods employed as well. The only plausible conclusion is that the vast majority of the guns used for homicide were the ones kept in the house.

Pro-gun advocates might try a different tack. If an angry spouse has a gun, the other might seek protection by buying a gun also. However, this strategy had to fail for the survey to find a correlation between gun ownership and homicide. This does nothing to rescue the pro-gunner's point that guns protect their owners.

What this objection is asking us to imagine is this: a gun prevents a murder from happening in, say, nine cases. But on the tenth it fails (by necessity, to produce the murder victim in question). If guns really provided this kind of protection, we could easily imagine that one of the previous nine murder attempts would have been successful, had the victim not possessed a gun. In that case, non-gun owners would have seen a higher murder rate. This is something the study would have found (see point 1), but it did not; it found a higher murder rate among gun owners. Pro-gunners might then argue that an individual facing a likely threat sought protection by buying a gun, hence the higher correlation. But this is the same argument rebutted in point 3. Ultimately, the pro-gunners starting assumption is incorrect. Guns do not prevent a series of threats, one of which ultimately succeeds; rather, guns enhance the possibility of murder.

If there is an Illogic Hall of Shame, this remark deserves to be emblazoned above its front entrance. By this reasoning, we shouldn't put seat belts in cars, because people killed in car crashes were susceptible to those accidents anyway.

What Blackman is doing here is evoking a general risk for murder, while ignoring its specific risk multipliers. You may, in general, have an antagonistic person in your life given to flashes of murderous temper. But there are specific factors that may increase the risk of murder. Does he drink? Use drugs? Commit crime? Own a gun? Increasing any of these behaviors increases the risk. But it makes no sense to increase the risk multiplier, let someone get murdered, and then argue that the multiplier was not at fault, since the victim was obviously susceptible to murder anyway.

This argument also ignores one of the study's findings, that a gun in the home increased the risk of gun homicide only, and not any other method of homicide.

This is a variation of the Blackman argument above. Water is not the only thing correlated with drowning. There are all the usual risk multipliers, such as a lack of lifeguards, life jackets, warning signs, adult supervision, etc. And notice that this analogy is incorrect. The analogy of guns isn't to water; it's to a lack of lifeguards. The analogy to water is actually murder in general.

Homes that kept guns experienced an increase in homicides, but this increase was entirely due to gun-related homicides, not homicides by any other method. This objection misses the point.

These cases were rare, but even so, this objection is irrelevant. The protective benefits of a gun would have still shown up in the different victimization rates of gun-owning and gun-less households. (See point 1.)

Epidemiologists are highly experienced at using the case-control method to determine risk factors. This is how cigarette smoking was linked to lung cancer, for example. The statistical method is the same no matter what the risk factor, be it cigarettes, a virus, a missing vitamin or a gun. A good analogy is that of an astronomer using optics technology to make a breakthrough in optometry.

This objection is bogus, since it ignores the role of multivariate analysis.

But the survey controlled for criminal backgrounds and domestic violence. The gun/murder correlation was reached after multivariate analysis factored these variables out.

But the survey controlled for neighborhoods. The researchers matched the control subjects by neighborhood to the case subjects.

Again, this objection ignores that multivariate analysis factored out all these variables. The "2.7 times" statistic measures gun possession alone (within the limits of the study's 31 variables).

The survey asked questions about 31 variables, but in a complex world it's always possible to think up more. Kellermann asked about the most obvious ones; even then, only six retained significance in the final analysis. If there were indeed a "missing variable," it would have to be extremely strong -- and probably extremely obvious as well -- to produce a murder risk of 2.7.

Indeed, the study asked only "yes or no" questions about problems in the home. For example, it asked whether any member of the household had been arrested, without determining the severity of the criminal charge. However, just because the individual questions did not control for severity does not mean the entire study didn't, since it asked a total of 15 questions about behavior, many closely related to each other. But this is really an argument about refining the study's results, not overturning its conclusions, which would be highly unlikely.

Not true. After the researchers controlled for these other risks, the murder risk associated with guns increased, from 1.6 in the univariate analysis to 2.7 in the multivariate analysis. If the study had underestimated the amount of drug use or other domestic problems, then the true risk associated with guns would be even greater.

If this were true, this would indeed artificially raise the murder risk of having a gun in the home. Conversely, if the number of guns in the case homes were underreported, then this would artificially lower the murder risk associated with guns. But the authors do not believe this was a problem. First, in two of the three counties they studied, they compared their survey results to a pilot study of homes listed as the addresses of owners of registered handguns. The survey respondents' answers were found to be generally valid. Second, the rate of gun ownership by the control respondents in all three counties was comparable to estimates derived by previous social surveys and Cook's gun-prevalence index. (6)

Of course, respondents might not have disclosed possession of illegal guns. Pro-gunners argue that the case subjects were prevented from underreporting the possession of such guns, because murder itself is almost impossible to underreport. (It's difficult to hide either a corpse or a person's absence). And a murder causes the police to search -- and usually find -- the murder weapon, so the facts of gun ownership in the case homes tended to come out. However, control subjects have not been investigated by the police for guns, nor do they desire such a search, so they may lie about possessing an illegal gun. The researchers were aware of this possibility, and they assured the respondents that their answers were confidential, and that they could freely refuse to answer any questions. Even so, only a very few respondents refused to answer a question. Ultimately, the possibility of underreporting remains pure speculation at the moment, and further research needs to clarify this question.