Critical Commentary on a Paper by Lott and Mustard

by Stephen Teret

August 8, 1996

The Johns Hopkins Center for Gun Policy and Research

Laws that help determine whether people carry concealed weapons may affect the incidence of gun deaths in this country. These laws, therefore, deserve the most careful and scientifically accurate evaluation. The Johns Hopkins Center for Gun Policy and Research and its affiliated experts have carefully reviewed the paper by John R. Lott, Jr. and David B. Mustard on the impact of "shall issue" laws, which require officials to issue permits to carry concealed firearms. We find the authors' clams that such laws deter violent crimes to be unsubstantiated. Their study contains factual and methodological flaws, and reaches conclusions that are implausible based on criminologic research and theory. Some of the most important problems with Lott and Mustard's study are outlined below.

The study uses incorrect and discredited methodology. The results of any study are influenced by the type of statistical techniques used by the researchers. The technique used in most of Lott and Mustard's analyses has been deemed by criminologists and econometricians since the early 1970s to be inappropriate for this type of study. The validity of the statistical techniques chosen by Lott and Mustard depend on the assumption that data used in the study (such as crime rates in neighboring counties, and crime rates in consecutive years) are not related to each other. If, however, relationships exist, than false findings of statistical significance will occur.

Lott and Mustard use arrest rates to predict crime rates, and this too is problematic. For example, their estimate of the laws' effect on crime rates varies five-fold, depending on how the deterrent effects of arrest were measured. A National Academy of Sciences panel of experts determined nearly two decades ago that arrest and crime rates can not be sufficiently disentangled to permit analyses such as those used by Lott and Mustard.

The authors demonstrate that "shall issue" laws tend to be implemented when violent crime has recently increased. The reductions in violent crime that the authors attribute to the laws may simply be a commonly observed downward drift in crime rates toward some long-term average level. The authors failed to use state-of-the-art analytic techniques which would distinguish a true effect of the law from an expected downward drift towards average levels.

The study's results depart from well-established criminologic theory and facts about crime. "Shall issue" laws were adopted principally to deter predatory street crime, the most common example of which is robbery by a stranger. But Lott and Mustard's results indicate that "shall issue" laws had little or no effect on robbery rates. The strongest deterrent effects estimated were for rape, aggravated assault, and murder. But most rapes and aggravated assaults are committed by someone known to the victim - a situation in which carrying a concealed gun in public areas is less relevant. In addition, only 17% of murders are the result of predatory crimes.

Lott and Mustard argue that criminals, in response to "shall issue" laws, are substituting property crime for crimes likely to involve contact with victims, but the observed "substitutions" make little sense. No credible criminologic theory can explain why a criminal would steal a car because he felt deterred from assaulting someone.

The study does not account for the effects of other important gun laws. In some of the states that passed "shall issue" laws, other gun laws were also enacted during Lott and Mustard's study period. For example, between 1989 and 1991; Florida passed a law requiring all handgun purchasers to undergo a background check and a 3-day waiting period; Oregon lengthened its waiting period and required more detailed background checks; and, Virginia adopted an instant background check system for handgun purchasers (later extended to all firearms). These other laws may substantially affect homicide and other crime rates, yet Lott and Mustard fail to consider their effects.

Knowing the exact date each "shall issue" law took effect is critically important to measuring its impact -- yet the study includes some errors in these dates. For example, the authors claim that Virginia adopted its "shall issue" law in 1988. But that law continued to give courts considerable discretion over when to issue a concealed weapon carrying permit (and some populous counties issued very few permits). Only in 1995, in a much publicized move, did Virginia eliminate that discretion. Also, the authors assert both that Maine adopted a new "shall issue" law in 1985, and that Maine nevertheless had a law from 1977-1992. During the study period, Maine adopted changes to its concealed carry law in 1981, 1983, 1985, 1989, and 1991. The 1985 changes do not eliminate the rather subjective requirement that permits be issued only to persons with "good moral character."

The study does not consistently define what it is evaluating. Lott and Mustard describe a "shall issue" law as one that requires "permit requests be granted unless the individual has a criminal record or a history of significant mental illness...." Yet they classify as "shall issue" some state laws that do not fit this definition. For example, even the NRA (in its Internet materials) recognizes that authorities in Connecticut and Alabama retain some discretion over who gets a concealed weapon permit. This means Lott and Mustard may mix together states with quite different rules for granting a permit.

For more information contact Professor Stephen Teret, (410)955-3995.

*Established in 1995 with funding from the Joyce Foundation of Chicago, The Johns Hopkins Center for Gun Policy and Research is dedicated to reducing gun violence. The Center provides accurate information on firearm injuries and gun policy; develops, analyzes, and evaluates strategies to prevent firearm injuries; and conducts public health and legal research to identify gun policy needs.

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