Simon Chapman, PhD; Michael Stewart, PhD; Philip Alpers; Michael Jones, PhD
Disclaimer: Dr. Chapman was a member of the Australian Coalition for Gun Control, which advocates for firearm law reform, between 1993 and 1996. Mr. Alpers runs GunPolicy.org, a global nonpartisan clearinghouse for firearm-related data.
Disclosures: Disclosures can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M18-0503.
Reproducible Research Statement: Study protocol, statistical code, and data set: See the Supplement.
Summary of statistics.
Reported P values are 2-sided. The constant model assumes that the rate of mass shootings remains constant across the full period; the changepoint model assumes that the rate differs between the before and after periods. LR = likelihood ratio.
* January 1979 to June 1996.
† July 1996 to February 2018.
‡ Based on 20 million simulations; R code (R Project for Statistical Computing) is provided in the Supplement.
Open circles indicate mass shootings. Top. Occurrences of mass shootings, 1979–1996. Bottom. Estimated rate of mass shootings per year under 2 different models. Our statistical test compared the constant rate and changepoint models, rejecting the former in favor of the latter. The vertical dashed line indicates the change at June 1996.
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Chapman S, Stewart M, Alpers P, Jones M. Fatal Firearm Incidents Before and After Australia's 1996 National Firearms Agreement Banning Semiautomatic Rifles. Ann Intern Med. [Epub ahead of print 13 March 2018]:. doi: 10.7326/M18-0503
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Published: Ann Intern Med. 2018.
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