ating the DGU estimates from the various gun use surveys. We find that fundamental problems in defining what is meant by defensive gun use may be a primary impediment to accurate measurement. Finally, after reviewing the literature that attempts to count the annual number of defensive gun uses in the United States, we then consider the small set of studies that evaluate the effectiveness of firearms for defense.

COUNTING DEFENSIVE GUN USES

How many times each year do civilians use firearms defensively? The answers provided to this seemingly simple question have been confusing. Consider the findings from two of the most widely cited studies in the field: McDowall et al. (1998), using the data from 1992 and 1994 waves of the National Crime Victimization Survey (NCVS), found roughly 116,000 defensive gun uses per year, and Kleck and Gertz (1995), using data from the 1993 National Self-Defense Survey (NSDS), found around 2.5 million defensive gun uses each year.

Many other surveys provide information on the prevalence of defensive gun use. Using the original National Crime Survey, McDowall and Wiersema (1994) estimate 64,615 annual incidents from 1987 to 1990. At least 19 other surveys have resulted in estimated numbers of defensive gun uses that are similar (i.e., statistically indistinguishable) to the results founds by Kleck and Gertz. No other surveys have found numbers consistent with the NCVS (other gun use surveys are reviewed in Kleck and Gertz, 1995, and Kleck, 2001a).

To characterize the wide gap in the estimated prevalence rate, it is sufficient to consider the estimates derived from the NSDS and recent waves of the NCVS. These two estimates differ by a factor of nearly 22. While strikingly large, the difference in the estimated prevalence rate should, in fact, come as no surprise. As revealed in Table 5-1, the two surveys are markedly different, covering different populations, interviewing respondents by different methods, using different recall periods, and asking different questions.

The NCVS is an ongoing annual survey conducted by the federal government (i.e., the Census Bureau on behalf of the Department of Justice) that relies on a complex rotating panel design to survey a representative sample of nearly 100,000 noninstitutionalized adults (age 12 and over), from 50,000 households. To elicit defensive gun use incidents, the survey first assesses whether the respondent has been the victim of particular classes of crime—rape, assault, burglary, personal and household larceny, or car theft—during the past six months, and then asks several follow-up questions about self-defense. In particular, victims are asked:



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