More Guns = More Gun Homicides, Statistically Speaking
In 2008, we explored the issue of whether more gun ownership meant more or less gun violence. What we found, and it still holds true, was that some studies had shown a statistical relationship between those factors — areas with a higher prevalence of guns had higher prevalence of gun homicides and homicides in general. But studies haven’t been able to show a causal relationship — that the mere presence of guns, as opposed to other factors, caused the higher rates of gun violence. It’s doubtful, however, that a study could ever beyond-a-doubt prove a causal relationship.
As Sorenson explained, scientists can’t conduct a random experiment. So, instead, researchers are left with statistical models, which are “very fragile,” says Charles F. Wellford, who was chair of the committees that authored a lengthy 2004 report on this topic by the National Research Council of the National Academies. These models are subject to what control variables researchers use. “Everyone knows there’s other things than guns that cause crime,” says Wellford, a professor in the Department of Criminology and Criminal Justice at the University of Maryland. So these models become very complex and slight changes can cause very different results, he says.
The National Research Council review of the available research on guns and crime found that studies comparing similar geographic areas, such as urban areas to urban areas, known as “case-control studies,” showed that “violence is positively associated with firearms ownership.” But when looking at larger areas, such as countries, the National Research Council report found “contradictory evidence.” Both types of studies, said the report, failed to address factors involved in buying a gun — it’s not a random decision. And gun ownership data itself is lacking — it comes only from public opinion surveys.
Eighteen experts participated in the NRC report, including those in criminology, sociology, psychology, economics, public health and statistics. The NRC’s conclusion: “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.”
Wellford says the new literature that has emerged since that 2004 review “doesn’t change in any way the conclusions from our report.”
Why can’t a statistical relationship prove a causal one? There are many other factors besides the presence of guns. Adam Lanza, the shooter in the elementary school killings in Newtown, “had lots of things going on in his life and one of them was access to multiple weapons,” says Wellford, himself a gun owner. “It’s hard to parse out what the effect is of having the gun, but there’s no question there’s some effect.” But is it 2 percent, 10 percent, 100 percent of the causal model? “We don’t know.”
Hemenway, director of the Harvard Injury Control Research Center, says he would “bet a lot of money” that the prevalence of guns increases homicide, all other things being equal. “I think the evidence is very consistent with the notion that more guns have made us less safe.” But it’s “almost impossible” to prove a causal relationship. “All the data are consistent with a causal relationship, but it’s very hard to say anything is causal,” he says.
Hemenway and coauthor Lisa M. Hepburn reviewed research from peer-reviewed journals and found that the evidence from studies of U.S. cities, states and regions “is quite consistent … where there are higher levels of gun prevalence, homicide rates are substantially higher, primarily due to higher firearm homicide rates.” But, again, the 2004 report said: “None of the studies can prove causation. They merely examine the statistical association between gun availability and homicide.”
There’s also a chicken-and-egg question when it comes to gun violence. Did the violence come first, and then the guns followed, or the other way around?
“I don’t think any of us believe the arrow points in one direction,” says Garen Wintemute, director of the Violence Prevention Research Program at the University of California-Davis and an emergency room doctor. It’s “probably true that rising crime leads to a perception of increased threat and, therefore, an increase in the prevalence of gun ownership.” And it’s “also the case that making firearms more available is followed by an increase in firearm crime.”
A study by the Law Center to Prevent Gun Violence found that seven of the 10 states with the strongest gun laws — by its own definition — also had the lowest gun death rates. Of course, there’s a chicken-and-egg issue with gun control laws, too — it’s easier to pass gun control laws in areas that already had low gun ownership, and harder to pass them in areas with more gun owners.
One thing that is clear: Guns are effective lethal weapons. “If there were no guns, the lethality of crimes would be less,” says Wellford. “You can’t have a drive-by knifing.”
In all cases of injury prevention, says Hemenway, the agent, or method, involved makes a difference. On Dec. 14, the day of the shooting in Newtown, another attack occurred at an elementary school in China. The attacker there had a knife, and injured 22 kids and one adult. But no one was killed. Why the stark difference in fatalities? “The answer is the type of weapon they had,” Hemenway says.
The NRC report, like Sorenson, said that more research was needed. “The federal government has to invest some money in doing research on what role guns play in violence,” Wellford says.
When we spoke with Wellford in 2008, he cautioned against drawing conclusions from statistics that didn’t prove causation. “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,” he said.