October 20, 2009

Volokh: Criticism of "Guns Did Not Protect Those Who Possessed Them from Being Shot in an Assault”

UCLA Law Professor Eugene Volokh, writing on his blog, The Volokh Conspiracy, recently critiqued the bad science and mistaken statistical conclusions in a press release posted on ScienceDaily.com. The release, entitled "Guns Did Not Protect Those Who Possessed Them from Being Shot in an Assault,” is the title of a misleading study by Charles C. Branas, PhD, Associate Professor of Epidemiology at Penn.

Volokh wrote:

The Branas study estimated that people with a gun were 4.5 times more likely to be shot in an assault than those not possessing a gun.

Eugene Volokh

Courtesy, The Volokh Conspiracy

Eugene Volokh

“This study helps resolve the long-standing debate about whether guns are protective or perilous,” notes study author Charles C. Branas, PhD, Associate Professor of Epidemiology. “Will possessing a firearm always safeguard against harm or will it promote a false sense of security?” …

Penn researchers investigated the link between being shot in an assault and a person’s possession of a gun at the time of the shooting. As identified by police and medical examiners, they randomly selected 677 cases of Philadelphia residents who were shot in an assault from 2003 to 2006. Six percent of these cases were in possession of a gun (such as in a holster, pocket, waistband, or vehicle) when they were shot.

These shooting cases were matched to Philadelphia residents who acted as the study’s controls. To identify the controls, trained phone canvassers called random Philadelphians soon after a reported shooting and asked about their possession of a gun at the time of the shooting. These random Philadelphians had not been shot and had nothing to do with the shooting. This is the same approach that epidemiologists have historically used to establish links between such things as smoking and lung cancer or drinking and car crashes.

This was promptly echoed in the Philadelphia Daily News.

Conspicuously missing from the press release and the news story were two critical limitations that were admitted in the original study. These qualifiers mean that the press release headline, as well as all the other statements and implications of causation, were quite mistaken. Perhaps defensive possession and carrying of guns helps protect the possessor and carrier, and perhaps it doesn’t. But the study sheds virtually no light on the subject.

1. To begin with, there’s the obvious causation/correlation problem. Maybe, as the authors speculate, carrying a gun increases your chances of being shot with a gun (as suggested by the framing of the issue as “whether guns are protective or perilous”), or at least fails to decrease them (”guns did not protect”). Or maybe a third source — perhaps some people’s being the targets of death threats, or being in a dangerous legal line of work, or being gang members or drug dealers — causes both higher gun carrying among those people and higher risk of being shot.

By way of analogy, we don’t suggest that pacemakers cause heart attacks, or don’t protect against heart attacks, just because we find a correlation between the presence of pacemaker and the incidence of heart attacks. Obviously, people might get pacemakers precisely because they’re at risk of heart attacks. Well, people might get guns precisely because they’re at risk of attack. (Stewart Baker makes a similar point.)

One can try to control for this in some measure — but while the study controls for some relevant attributes (race, sex, age, neighborhood, having a “high-risk occupation,” and having at least one arrest on one’s record), it leaves a vast range of factors uncontrolled. You’d think that gang members are more likely than others to carry guns and to get shot, even controlling for the presence of an arrest record. (Lots of law-abiding people carry guns, but I expect that more gang members do.) But the study doesn’t control for that, or for many other things.

Let me illustrate this with a deliberately oversimplified model.

To read the rest of the piece, click here :

Comments (4)

These scientists remind me of Mr. Obama.They get their stories in the TWIST,SPIN, TELL format.There is no straightforward, honest, or even simple reporting anymore when it comes to gun issues. Keep em honest Lee W .........

Posted by: Sharps | October 22, 2009 11:10 AM    Report this comment

Due to the inaccurate study, the article would suggest they were not talented scientists. They were more like scientists who's honest work was not good enough to put bread on the table so they had to search out other opportunities.

Posted by: JWallace | October 22, 2009 12:50 AM    Report this comment

Isn't this also a clear case of the fallacy of sampling on the dependent variable?

Sampling gun shot victims to infer the effects of gun-carry, is like sampling drug addicts and to infer the effects of some prior behavior (e.g., carrot eating, milk drinking, or television watching).

Such a study may be useful for DEVELOPING hypotheses, but it is not useful for TESTING them. (Apologies for shouting.)

Posted by: DrNo | October 21, 2009 10:44 AM    Report this comment


Issac Asimov was a man of many talents. Famous principally for his prodigious body of science fiction literature, he began his career in chemistry, in which field he held a PhD. Back in those days, in order to work at the PhD level, a student literally had to become a scientist and produce work which added to the body of knowlege in that field. Asimov believed in his core that the ethical standards of a true scientist hold him to the pursuit of good, honest, and open science. He reserved his most venomous hatred for those scientists, particularly chemists, who perverted their science for unethical gain.

The five people who authored this study, led by Charles C. Branas, PhD, Associate Professor of Epidemiology at Penn, have done exactly what Issac Asimov hated most. They took money from the Joyce Foundation, a notoriously generous funder of anti-gun studies, and they sold their skills, talents, education, training, experience, and morals to the Joyce Foundation to produce an anti-gun study, and in the process, they deliberately perverted their scientific work for monetary gain.

In a just society they would be properly recognized and rewarded for their work. People who sell themselves for money are not called scientists.


Posted by: Lee W | October 20, 2009 5:40 PM    Report this comment

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