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Are Active Shootings Temporally Contagious? An Empirical Assessment


“Active Shootings,” which include shootings in public, confined areas such as schools, often traumatize communities and attract intense media coverage. Proposed policy responses to the phenomenon, such as concealing information as to casualty counts and even the identities of shooters, often suppose that active shootings are “contagious,” in that previous occurrences can enhance the likelihood of subsequent occurrences. This study marks the first attempt at assessment of the contagiousness of the active shooting phenomenon, and deploys a statistical model—the series hazard model—that is well-suited to the substantive issue of contagion as well as the fine-grained nature of the active shooting data. Results indicate that the hazard of observed active shootings was a function of the number of active shootings that preceded them in the previous two weeks.

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  1. Given the relatively small sample size, monthly dummies were avoided in order to limit the number of independent variables in certain models.

  2. In order to avoid dropping the four cases with missing values on age, the mean value (36.80) was imputed.

  3. A word about the “marginal significance” of the “number of active shootings in the last two weeks” contagion variable is perhaps in order. Some scholars prefer to disregard findings of marginal significance while others are willing to substantively interpret such findings, at least under certain conditions. Several reasons can be offered in support of interpreting the marginally significant effect of this variable. First, the present researcher judged that on balance, given the literature review and that active shootings and contagion have heretofore not been studied, it was best to operate with a two-tailed test. Other researchers, however, might quite reasonably disagree and hold that a one-tailed approach should have been adopted—perhaps, for example, because of different perspectives on the literature review, or perhaps because the contagion construct has deep roots in learning theory, which has empirically exhibited noteworthy explanatory power in a wide array of criminological studies.

    Second, it might be reasonable to suppose that in view of the magnitude of the impacts active shootings can have on communities together with the amount of resources devoted to the active shooting problem, and the potential effect of policy responses on civil liberties as well as safety, a bright line, summary distinction between p=.07 or .09 and p=.05 is not the best way to proceed. In short, considerations of “practical importance” might justify substantive interpretation of the contagion findings in this study.

    In light of the above, interpretation of contagion results is offered, followed by a discussion of the findings regarding the incident characteristics.


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Kissner, J. Are Active Shootings Temporally Contagious? An Empirical Assessment. J Police Crim Psych 31, 48–58 (2016).

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  • Active Shootings
  • Active Shooters
  • Contagion
  • Series Hazard Model