Suicide, Homicide and Guns

There are a number of reasons social psychologists are confident that the availability of firearms is a major cause of violent death. In an earlier post, I discussed some of the many studies of the priming effect of weapons on aggression. These studies suggest that the presence of weapons, or pictures of weapons, increases aggressive thoughts and behaviors. Since these are laboratory experiments in which participants are randomly assigned to conditions, they permit a relatively strong inference of causality. However, due to the obvious constraints on our willingness to provoke aggression in the lab, some people find these studies to be artificial, and feel more comfortable with field studies of the availability of firearms in the real world.

Many of these field studies are ecological, in the sense that they measure both the availability of weapons and the number of deaths at the aggregate or population level. For example, in an early study, Archer and Gartner (1987) found that the homicide rate in countries around the world is highly correlated with the availability of handguns. But correlation does not mean causation, and the countries involved in this comparison differed in many other ways besides their weapons policy. Most recent studies have attempted to statistically control for alternative explanations such as urbanization, poverty, alcohol use, depression, etc. However, since the number of alternative explanations is theoretically infinite, there are limits to this approach.

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Gun advocates also attack the validity of the measures used in these studies. For example, in most studies, the availability of firearms is determined from gun registration statistics. However, it could be argued that many homicides are the result of unregistered guns in the hands of criminals. Can this assumption account for the positive correlation between gun availaility and murder? Yes, but only if you assume that those areas that contain the most legally registered guns also contain the most illegal ones.

A more time-consuming but more conservative procedure is to start with a suicide or homicide and work backward, looking at each individual case. In these observational studies, for each suicide or homicide victim, regardless of the manner of death, it is determined whether firearms were available in the home. These people are compared to a matched control group of people who did not commit suicide or were not murdered, such as participants in a national health survey. This allows you to compute a likelihood ratio—the likelihood of a homicide or suicide when a gun is available compared to the likelihood when it is not.

In a study published this week, Andrew Anglemyer of the University of California at San Francisco and his colleagues did a thorough literature search and located 15 such observational studies. They then did a meta-analysis of these data. A meta-analysis is an analysis of analyses, a way of statistically combining the results of several studies to estimate the size of an effect. These were their findings:

• You are 3.24 times more likely to commit suicide when a firearm is readily available than when it is not. These findings do not differ for men and women.

• You are 1.94 times more likely to die of a homicide with a gun in the home than without. This effect differs for male and female homicide victims. Women are 2.94 times more likely to be killed when a firearm is available, while for men, the effect is almost nil—only 1.29 times more likely.

The meta-analysis shows that having a firearm available has a greater influence on suicides than on homicides. This makes sense, because most firearm suicides kill themselves with their own gun, while most firearm homicide victims are killed with someone else's gun.

The homicide data show that firearm availability only increases the risk for female victims. Other studies show that women are most likely to be murdered by someone they know. This suggests that firearm availability makes it easier for domestic violence to become lethal. On the other hand, there is no evidence that owning a firearm increases the risk of homicide for men, since they are usually not killed with a gun belonging to themselves or a family member.

In an accompanying editorial, David Hemenway, a leading authority on firearm victimization, points out that this pattern of results is due to Anglemyer's choice to analyze only individual-level, observational studies. He argues that the meta-analysis substantially underestimates the effects of firearm availability on male homicides because it only asks whether the victim had access to a gun, when the more important question is whether the perpetrator had access to a gun. Therefore, he suggests that future studies of homicides be either population-level ecological studies which measure the number of guns in the community, or individual-level observational studies of the availability of firearms to perpetrators rather than victims.

You may also be interested in reading:

Symbolic Racism and Gun Ownership

Open Carry

Breathing While Black

I Cough in Your General Direction

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New international research has shown that particulate air pollution (or soot) is a significant cause of low birth weight in infants. The study is actually a meta-analysis of 14 studies done in nine countries, with a total sample of over 3 million births. A meta-analysis is an analysis of analyses, or a way of statistically combining the results of several studies to arrive at an overall estimate of the significance of an effect. The fact that the studies were done by different researchers, at different sites, using slightly different research methods is generally seen as increasing our confidence in the outcome.

Pollution at the study sites varied from 10 to 70 micrograms per cubic meter of air. The effect was small but consistent. Two ways of summarizing the results are:

• For every 10 microgram increase in pollution, average birth weight declines by 8.9 grams, or roughly one-third of an ounce.
• For every 10 microgram increase, the probability that an infant will be of low birth weight—less than 5 pounds, eight ounces—increases by 3%.

The effect was highly significant when controlling for the socioeconomic status of the mother and other confounding variables.

The two major sources of particulate pollution are industrial plants, especially power plants, and vehicle emissions. Exposure has been shown to be associated with health problems such as asthma, heart disease, stroke and diabetes. It's not clear why particulate pollution reduces birth weight, but one possibility is that it, and the diseases with which it is associated, place stress on the mother's body, which affects fetal growth. Low birth weight is a risk factor for infant mortality, and for heart, lung and behavior problems in later life.

A recent article in The Lancet attempted to quantify the major causes of premature death in the world. Air pollution was #7, contributing to 3.2 million deaths per year. (In case you're wondering, high blood pressure is #1, smoking #2, and alcohol consumption #3.) As David Pettit of the Natural Resources Defense Council notes:

Fortunately there are many actions that can be taken to address outdoor air pollution. The technology is readily available at a fraction of the investment cost compared to the health costs that the public bears.

Obviously, the availability of clean air technology is of little consequence if the corporations responsible for most of the pollution control a corrupt political system.

As if to show how obsolete our political system is, last August, the U. S. Court of Appeals struck down an Environmental Protection Agency rule intended to reduce emissions crossing state borders, partially on grounds that the rule was a violation of states' rights.