-Caveat Lector- Doctoring Gun Data <http://www.stats.org/newsletters/0103/doctorgun.htm> If guns are a public health problem, it's best to apply public health standards to gun research March 2001 Violent crime is a serious issue. Violence involving the misuse of firearms is all the more serious because of the lethal nature of the weapons. Given the social cost to the community of the medical consequences of gun violence, it is not unreasonable that doctors should have a role in investigating the problem. As a result, a considerable body of research on the subject has been published in medical journals. However, once proper medical standards are applied in interpreting such research, the evidence often seems less convincing, from a medical standpoint, than it does from a criminological point of view. One recent example resulted in the headline "Gun control law helped cut crime, study says," in the LA Times. The San Francisco Chronicle declared, "Handgun limit law succeeding" (both Feb. 28). These banners ran in response to a report in the Journal of the American Medical Association (JAMA) that investigated the effectiveness of a 1991 California law denying handgun purchases to violent "misdemeanants" (as the study termed those who had previously been found guilty of misdemeanor offenses). The study's authors compared the arrest rate of those "misdemeanants" who had their handgun purchases approved before the law to those who were denied after it was passed. They concluded that denial was "associated with a specific decrease in risk of arrest for new gun and/or violent crimes." But if guns are looked at as a public health problem, then the standards that would be applied when looking at risks for disease need to be used. When that is done, it may turn out that those headlines were jumping the gun. The first issue is whether someone who was allowed to purchase a gun is at a significantly greater risk of committing a crime compared to someone who was denied purchase. Doctors measure such things using "relative risks." These risks are measured by odds ratios, and the study found an odds ratio of 1.15:1 for the handgun purchasers. This means that for every 100 people not allowed to buy a gun but who nevertheless committed a crime, 115 people who had been allowed to do so broke the law. Relative risk is a tricky area in medical science, because it is hard to filter out other factors that may affect the result. Epidemiologists are therefore loath to consider small relative risks as indication of any strong link between the disease and the possible cause. A relative risk of 1.15 is very small and would therefore be ignored by experts. The study's authors did so, to their credit. What they considered significant, however, was the relative risk for committing gun and/or violent crime specifically, which they calculated at about 1.3:1. But even a 30 percent greater risk like this would be regarded as minuscule by epidemiologists. In fact, they normally require a difference of 200-300 percent before concluding that they have evidence of cause and effect (the relative risk for lung cancer among smokers, for instance, is roughly 300:1). The relative risk at issue here does not meet the medical standards for real concern about cause and effect. Therefore the claim that it is the handgun purchase that makes the difference cannot be made with any real certainty. Furthermore, when an epidemiologist looks at the cause of a disease and discovers a slightly elevated risk among, say, left-handed people, he does not stop there. He looks further and asks whether it affects all left-handed people or predominantly left-handers with bad eyesight, for example. Most left-handers could actually be less susceptible to the disease, but the overall risk for the group as a whole could be increased by the disproportionate effect in the sub-set of myopia sufferers. Was there such a disproportionate effect in this study? There certainly seems to be. The researchers split the "risky" population the "misdemeanants" who'd gotten guns and then committed crimes into about 30 sub-groups, depending on age, number of prior convictions and number of prior convictions for gun and/or violent crime. Of these, only three groups came out with relative risks enabling the researchers to say with any confidence that they would be more likely to commit crimes. They were "misdemeanants" arrested for gun and/or violent crime who were either aged 30-34 (a relative risk of 1.64), who'd had four or more prior convictions of any sort (a relative risk of 1.8), or who'd been convicted for one gun and/or violent crime previously (interestingly, more prior convictions for these crimes meant less of a chance of arrest). All the other sub- categories possessed either an approximately equal or lesser chance of arrest. These findings seem pretty clear. They point to a conclusion that habitual minor criminals are more likely than others to commit gun and/or violent crime. It is also important to bear in mind that "gun and/or violent crime" need not necessarily involve a firearm a drunken bar fight would qualify just as much as armed robbery. The role of legal gun purchase in leading to such an eventuality is far from clear (in epidemiological terms, there is no "biological pathway" here). From the evidence the researchers uncovered, then, it might actually be possible to argue that the California law forbids many people handgun purchase for no reason. Because certain categories of former offenders are shown to be less likely to commit crime when allowed access to firearms, the evidence could be interpreted as demonstrating that allowing such people access would be a useful public safety measure. But such a conclusion would be just as shaky as the conclusion that the law reduced crime. If the role of guns in violence is to be examined from an epidemiological standpoint, the rigorous standards normally used in that field should be used. Drawing conclusions from the evidence that cannot stand up to detailed scrutiny does not necessarily help advance the cause of public safety. <A HREF="http://www.ctrl.org/">www.ctrl.org</A> DECLARATION & DISCLAIMER ========== CTRL is a discussion & informational exchange list. Proselytizing propagandic screeds are unwelcomed. 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