Q: Are violent crimes more or less common in areas where handgun ownership is higher?
A: Some studies have found that murder rates (not crime rates in general) are higher where guns are more prevalent. But social scientists have not found a direct causal relationship between the two factors.
This question is one raised by both those who advocate fewer restrictions on gun ownership and those who call for stricter controls. The former group hopes to prove that more guns do not equal more crime (or even could lead to less crime due to guns being used for protection or self-defense). The latter group hopes to prove that lower rates of gun ownership mean less crime occurs. But major studies on the topic have not found a cause-and-effect relationship between the two factors, though they have found statistical relationships.
David Hemenway, director of the Harvard Injury Control Research Center and the Harvard Youth Violence Prevention Center, notes that most types of crime don’t necessarily involve guns – car theft or muggings or rape, for instance. But other crimes, such as murder, often do. Studies that have looked at gun ownership and murder rates, he says, have shown "yes, there’s a strong relationship." Such studies, Hemenway says, have controlled for certain variables, comparing urban areas to other urban areas or households in violent areas to other households in violent areas. With those types of studies, "the evidence is very compelling." There’s more gun murder in areas with more guns, and more murder overall, he says.
That’s not to say that taking the guns away from such areas would necessarily lead to a reduction in the murder rate. Such studies have shown a statistically significant relationship between guns and murder but not a causal one.
One of Hemenway’s studies, published in 2004 and coauthored by Lisa M. Hepburn, reviewed commonly cited research from peer-reviewed journals. It found that studies of the United States or U.S. cities, states and regions "generally find a statistically significant gun prevalence-homicide association." The report said that the evidence from such "U.S. cross-sectional studies is quite consistent … where there are higher levels of gun prevalence, homicide rates are substantially higher, primarily due to higher firearm homicide rates." Hemenway’s report also found that international studies "typically show that in high-income countries with more firearms, both men and women are at higher risk for homicide, particularly firearm homicide." So where there are guns, there is likely a higher rate of murders committed with guns in particular. However, the report noted, "None of the studies can prove causation. They merely examine the statistical association between gun availability and homicide."
In fact, major studies on this issue have not shown cause-and-effect – that the presence of guns causes more murders to occur (or crime in general) – which is certainly a more difficult hypothesis to test. The National Research Council of the National Academies in 2004 released a lengthy study of the available research on this issue, with the aim of finding whether a causal relationship existed. It didn’t find one, and it said that the available research itself was lacking. "In summary, the committee concludes that existing research studies and data include a wealth of descriptive information on homicide, suicide, and firearms, but, because of the limitations of existing data and methods, do not credibly demonstrate a causal relationship between the ownership of firearms and the causes or prevention of criminal violence or suicide," said the report, which was conducted by the NRC’s Committee to Improve Research Information and Data on Firearms, and Committee on Law and Justice. There were close to 40 members of the committees, including experts in criminology, sociology, economics, psychology, public health and public policy, and statistics.
Proving Cause and Effect
The National Academies report noted that drawing a causal inference is "always complicated and, in the behavioral and social sciences, fraught with uncertainty."
Charles F. Wellford, chair of the committees that authored the report and a professor of criminology at the University of Maryland, says it’s the causal relationship that people are interested in when the question of guns and crime is broached. "While scientists can make the distinction between association and causation, in the real world the interest is in the latter," Wellford tells FactCheck.org, noting that this is his opinion, not the panel’s. "Work that knowingly reports findings that do not meet a causal test knowing they will be used as if they do can only produce confusion especially in such contentious issues."
The report said that "case-control studies" (the urban-area-to-urban-area type of comparisons) "show that violence is positively associated with firearms ownership." What the National Academies calls "ecological studies" (those comparing large areas, such as countries) "provide contradictory evidence on violence and firearms." But neither have shown a causal relationship. Both studies fail to address the multiple factors involved in the decision to buy a gun – owning a gun is not a random decision, said the report. And data on gun ownership may be insufficient (such numbers are based on surveys). It also faulted ecological studies that look at large geographic areas, saying, "there is no way of knowing whether the homicides or suicides occurred in the same areas in which the firearms are owned."
In comparing the United States to industrialized democracies, the Academies says data show the U.S. has the highest rate of homicide and firearm-related homicide. But this also raises a chicken-and-egg question. "A high level of violence may be a cause of a high level of firearms availability instead of the other way around."
– Lori Robertson
Hepburn, Lisa M. and David Hemenway. "Firearm availability and homicide: A review of the literature." Aggression and Violent Behavior. Vol. 9, 2004: 417-440.
National Research Council of the National Academies, Committee on Law and Justice. "Firearms and Violence: A Critical Review." The National Academies Press: Washington, D.C., 2004.