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Firearms and Violence: A Critical Review
1. Published studies. There is no question that the empirical results on the effects of right-to-carry laws on murder (and other crimes) are sensitive to seemingly small variations in data and specification. Indeed, Wilson agrees that a few studies find positive effects of right-to-carry laws on murder. We cite four studies in Tables 6-3 and 6-4: Ayres and Donohue, Black and Nagin, Moody, and Plassmann and Tideman (cited in Chapter 6). There are almost certainly others not reported in these tables.
The rest of the committee and Wilson agree that fragility does not prove that the results of any specific paper are incorrect. However, some of the published results must be incorrect because they are inconsistent with one another. The important question, therefore, is whether the correct results can be identified. The rest of the committee thinks that they cannot. Contrary to Wilson’s claim, the committee did assess the existing body of empirical literature on right-to-carry laws (see the section beginning on page 127 and Tables 6-3 and 6-4). As described in the report, all of the empirical research on right-to-carry laws relies on the same conceptual and methodological ideas (page 121). Relative to the basic models estimated by Lott, some researchers used data from more counties and some from fewer; some used hybrid linear models while others used nonlinear specifications; some provide state-specific estimates while most provide a single national estimate; some added control variables while others used relatively parsimonious specifications; and so forth. All of the studies described in the literature review made plausible cases for their choices of models and data. Wilson seems to argue that a careful evaluation of the literature would reveal which paper or papers obtained correct results, but he does not suggest the evaluation criteria. The rest of the committee does not think that application of any scientific criteria to existing papers would identify the effects of right-to-carry laws on crime.
2. Committee control variable analysis.Chapter 6 shows that when the trend and dummy variable models do not include demographic and socioeconomic covariates (but do include year and county dummy variables) the estimates are relatively small, positive in one case (Table 6-6, Row 3), and statistically insignificant in all cases. Contrary to Wilson’s assertion, the chapter does not claim that this or any other specification is correct. Rather, this finding simply reveals that “detecting the effect, if any, of right-to-carry laws requires controlling for appropriate confounding variables.” In light of the fragility revealed in the literature, the fundamental issue is which set of covariates is sufficient to identify the effects of right-to-carry laws on homicide and other crimes. The importance of controlling for the correct set of covariates is well known. In fact, much of the debate between Lott and his statistically oriented critics focuses on determining the correct set of control variables. Everyone (including Wilson and the rest of the committee) agrees that control variables matter, but there is disagree-