Does gun control reduce crime or does crime increase gun control?

• Author: Moorhouse, John C.

Advocates argue that gun control laws reduce the incidence of violent crimes by reducing the prevalence of firearms. Gun laws control the types of firearms that may be purchased, designate the qualifications of those who may purchase and own a firearm, and restrict the safe storage and use of firearms. On this view, fewer guns mean less crime. Thus, there is a two-step linkage between gun control and crime rates: (1) the impact of gun control on the availability and accessibility of firearms, particularly handguns, and (2) the effect of the prevalence of guns on the commission of crimes. The direction of the effect runs from gun control to crime rates.

Conversely, because high crime rates are often cited as justifying more stringent gun control laws, high rates may generate political support for gun regulations. This suggests a causal effect running from crime rates to more stringent gun laws. But because both relationships between gun control and crime rates unfold over time, they are not simultaneously determined in the usual econometric sense. For example, crime rates in the early 1990s could be expected, ceteris paribus, to influence the stringency of gun control measures in the late 1990s. In turn, more stringent gun control in the late 1990s could be expected, ceteris paribus, to affect crime rates several years later. Using state-level data, this article provides estimates of these twin relationships between gun control and crime rates.

Measuring the Degree of Gun Control

Researchers attempting to estimate the effect of gun control on crime rates face two problems. First, how is gun control to be measured? What is the empirical counterpart to gun control? Gun control is an umbrella term covering everything from laws prohibiting the ownership of defined classes of firearms to mandating the inclusion of gun locks with every firearm sold. These measures represent discrete legislative acts passed on different dates by different governing bodies. How do they interact to control the availability of firearms? Are the various measures complements or substitutes?

Second, the effectiveness of a particular gun control statute depends not only on its being on the books but the degree to which the law is enforced. Two jurisdictions may have the same gun control statute but experience very different effects, because in one of the jurisdictions little effort is devoted to enforcing the regulation. Enforcement of gun laws must be taken into account in order to accurately assess gun control.

One contribution of this study is that it addresses these problems by using a comprehensive index of gun control laws for the 50 states and the District of Columbia. The index includes those laws in place in 1998. Normalized to take on values of 0 to 100, the index is based on 30 weighted criteria applied to six categories of gun control regulations. The index was constructed as a project of the Open Society Institute's Center on Crime, Communities and Culture. (1) The index "concentrates on states because most gun laws are state laws, though federal law also plays an important role" (Open Society Institute 2000: 1). Because our study uses cross-sectional data by state, to match up with the index, federal laws are treated as a constant across all states and the District of Columbia. (2) Another reason for focusing on states is that 40 states prohibit or restrict local governments from enacting gun control ordinances.

Although there are literally thousands of state and local gun control statutes, the authors of the index group specific gun control measures into the following six categories. (1) Registration of firearms including purchase permits and gun registration of handguns and long guns (rifles and shotguns). (2) Safety training required before purchase. (3) Regulation of firearm sales including background checks, minimum age requirements for purchasing a firearm, a waiting period before a sale can be completed, one-gun-a-month limitation on purchases, all applied to long guns and/or handguns, plus a ban on "Saturday night specials," junk guns, and assault weapons. (4) Safe storage laws including child access prevention law. (5) Owner licensing for possession of handguns and/or long guns and minimum age restrictions for gun possession. (6) The presence of more restrictive municipal and county ordinances.

In addition, the index takes into account whether or not a law is effectively enforced. For example, while 32 states require background checks going beyond federal requirements, a number have no mechanism for ensuring that checks are made. (3) Thus, the index distinguishes among states with no law, those with unenforced provisions, and those where the law is enforced. Furthermore, "In general, more points were assigned to 'upstream' measures [e.g., gun registration] than to 'downstream' measures [e.g., safe storage laws], to restrictions on handguns than to long guns, and to measures that facilitate the enforcement of the laws" (Open Society Institute 2000: 12). Each of the 30 criteria was weighted from 0 to 7. For example, gun registration receives a maximum of 7 points down to 0 for no state registration. A waiting period of more than three days for handgun purchases receives 6 points, while having no waiting period is scored 0. Information used in constructing the index was gathered in three stages: analysis of primary sources, cross-checking with the principal secondary sources, and verification with law enforcement and state agencies (Open Society Institute 2000: 14-16).

Finally, if one wishes to study the effects of state gun control laws, using a carefully constructed index of gun control laws has several advantages. First, the effectiveness of a state's gun control laws may not be independent of the gun control regime of neighboring states. If the citizens of state A can readily purchase guns in state B, then a spill-in effect may exist. Using an index provides a straightforward way of controlling for an adjacent state's gun control regime and estimating any spill-in effect.

Second, using an index also offers several statistical advantages. The obvious substitute for an index is a vector of dummy variables representing specific state statutes and for each the degree of enforcement. Unfortunately, the latter approach uses too many degrees of freedom given the sample size and the other control variables included in the analysis. Moreover, an index avoids the problem of collinearity among gun control measures (Kleck 1991: 401). Arguably, using dummy variables does permit analysts to be more specific in their assessment of the effectiveness of individual gun control regulations. An index confines analysts to commenting on the efficacy of a gun control regime as a whole.

Literature Review of Gun Control Studies Using State Data

In 1993, Kleck and Patterson surveyed the then contemporary literature on the effects of gun controls on crime rates. As part of this larger survey, the authors review 1:3 studies that use state data. They observe that two studies find that gun controls reduce violent crimes, two have mixed results, and nine find no reduction in crime because of gun control (Kleck and Patterson 1993: 254).

A conspicuous characteristic of early studies is the failure to include relevant control variables. For example, Newton and Zimring (1970) conclude on the basis of a positive zero-order correlation between gun ownership and firearm-related violence that gun control reduces violent crimes. They specify no ceteris paribus conditions. Seitz (1972) provides one of the more outlandish examples of an empirical study suffering from omitted variables. He begins by observing that "Today, few would deny that some relationship exists between firearms and violent death and crime" (Seitz 1972: 595). Using state observations, his evidence of the relationship between guns and crime is a 0.98 simple correlation coefficient between firearm homicides and total homicides. Seitz (1972: 597) displays the data on a scatter diagram with firearm homicides measured on the vertical axis and total homicides on the horizontal axis. He concludes, from the correlation, that a reduction in the prevalence of guns would reduce the number of homicides. This, of course, is no evidence for or against the efficacy of gun control. That the two measures of homicide are highly correlated is not surprising given that firearm homicides constitute more than 60 percent of all homicides in the United States (Jacobs 2002: 8). Seitz controls for no other variables that influence the number of homicides. Likewise, Phillips, Votey, and Howell (1976) using time series data, find a significant positive relationship between the stock of handguns per capita and the homicide rate. They include none of the usual social and economic variables thought to influence homicide.

Using state data and controlling for several social and economic variables, Sommers (1980) estimates the impact of two forms of gun control on seven categories of crime. GUN1 is a dummy variable taking on a value of 1 for states having a concealed weapons law and 0 otherwise. GUN2 takes on a value of 1 if the state has a licensing provision and 0 otherwise. Of the 14 estimated gun control coefficients, only 3 are statistically significant. In no case, is the concealment law found to have an effect. Commenting on Sommers' study, Magaddino and Medoff (1982: 50) argue that Sommers fails to take into account other forms of...