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Firearms and Violence: A Critical Review
ment on the correct set. Thus, the facts that there is no way to statistically test for the correct specification and that researchers using reasonable specifications find different answers are highly relevant. Given the existing data and methods, the rest of the committee sees little hope of resolving this fundamental statistical problem.
Furthermore, the example of the relationship between crime rates and policing in the dissent raises another problem. The usual way one proceeds in research is to estimate the relationship between two variables and if a significant relationship is found controls are introduced to test the relationship. As the dissent notes, these controls are selected based on reasonable theories and research. In this case, the bivariate relationship (between right to carry laws and crime) is small, positive in one case, and insignificant in all. This is not like the hypothesized conflicting bivariate findings in Wilson’s police example. Thus the selection of controls in the analysis of right-to-carry laws is as difficult as the committee contends
3. Committee trend model analysis. Wilson states that the trend model analysis in Table 6-7 estimates the effects of right-to-carry laws on a yearly basis, rather than a single trend.1 This is incorrect. The estimates reported in Table 6-7 are found using Lott’s trend model with restrictions on the number of postadoption years used in the analysis. If the model is correctly specified, this restriction should be inconsequential. However, we find substantial differences, especially for murder. In fact, when we restrict the number of postadoption years to five or fewer, the estimates switch from negative to positive. Thus, Model 6.2 appears to be misspecified. Moreover, despite Wilson’s assertion, these types of sensitivity test are commonly used in peer-reviewed journals and are suggested by Rosenbaum (2001) as a way to assess the robustness of an empirical model. Of course, results like those reported in Chapter 6 might often lead a paper to be rejected from a peer-reviewed journal.
Wilson further suggests that Lott’s findings may depend on the crime rate trends that changed dramatically over the course of the 1990s. All of the studies in this literature, however, attempt to control for trends in crime, and thus purport to reveal a time invariant effect of right-to-carry laws. If the effects vary by time, all of the existing models are misspecified.
In sum, we are encouraged that Professor Wilson agrees with the rest of the committee except for the specific conclusion regarding the effects of right-to-carry laws on murder. On this point, we find his arguments to be unconvincing and his summary of some parts of the chapter inaccurate. In our view the evidence on homicide is not noticeably different from that on other crimes evaluated in this literature and cannot be easily separated. If
Contrary to Wilson’s claim, the results in Table 6-7 all rely on models with covariates.