David M. Studdert, LLB, ScD; Yifan Zhang, PhD; Jonathan A. Rodden, PhD; Rob J. Hyndman, PhD; Garen J. Wintemute, MD, MPH
Acknowledgment: The authors thank the staff at the California Bureau of Firearms for providing the study data, and Karen Ding for research assistance. John Donohue, Jeremy Goldhaber-Fiebert, and Matthew Miller provided helpful comments on an earlier draft of the manuscript.
Disclosures: Authors have disclosed no conflicts of interest. Forms can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M16-1574.
Editors' Disclosures: Christine Laine, MD, MPH, Editor in Chief, reports that she has no financial relationships or interests to disclose. Darren B. Taichman, MD, PhD, Executive Deputy Editor, reports that he has no financial relationships or interests to disclose. Cynthia D. Mulrow, MD, MSc, Senior Deputy Editor, reports that she has no relationships or interests to disclose. Deborah Cotton, MD, MPH, Deputy Editor, reports that she has no financial relationships or interest to disclose. Jaya K. Rao, MD, MHS, Deputy Editor, reports that she has stock holdings/options in Eli Lilly and Pfizer. Sankey V. Williams, MD, Deputy Editor, reports that he has no financial relationships or interests to disclose. Catharine B. Stack, PhD, MS, Deputy Editor for Statistics, reports that she has stock holdings in Pfizer and Johnson & Johnson.
Reproducible Research Statement:Study protocol: Not applicable. Statistical code: The R code used to conduct the analyses is provided in Supplement 7). Data set: Not available.
Requests for Single Reprints: David Studdert, LLB, ScD, Center for Health Policy/PCOR, 117 Encina Commons, Stanford University, Stanford, CA 94305; e-mail, firstname.lastname@example.org.
Current Author Addresses: Drs. Studdert and Zhang: Center for Health Policy/PCOR, 117 Encina Commons, Stanford University, Stanford, CA 94305.
Dr. Rodden: Department of Political Science, Encina Hall West, Stanford University, Stanford, CA, 94305.
Dr. Hyndman: Department of Econometrics and Business Statistics, Wellington Road, Monash University, Clayton, Victoria 3168, Australia.
Dr. Wintemute: Department of Emergency Medicine, UC Davis Medical Center, 2315 Stockton Boulevard, Sacramento, CA 95817.
Author Contributions: Conception and design: J.A. Rodden, D.M. Studdert, G.J. Wintemute, Y. Zhang.
Analysis and interpretation of the data: R.J. Hyndman, J.A. Rodden, D.M. Studdert, G.J. Wintemute, Y. Zhang.
Drafting of the article: D.M. Studdert, Y. Zhang.
Critical revision for important intellectual content: J.A. Rodden, D.M. Studdert, G.J. Wintemute, Y. Zhang.
Final approval of the article: R.J. Hyndman, J.A. Rodden, D.M. Studdert, G.J. Wintemute, Y. Zhang.
Provision of study materials or patients: D.M. Studdert.
Statistical expertise: R.J. Hyndman, Y. Zhang.
Administrative, technical, or logistic support: D.M. Studdert.
Collection and assembly of data: D.M. Studdert, Y. Zhang.
Mass shootings are common in the United States. They are the most visible form of firearm violence. Their effect on personal decisions to purchase firearms is not well-understood.
To determine changes in handgun acquisition patterns after the mass shootings in Newtown, Connecticut, in 2012 and San Bernardino, California, in 2015.
Time-series analysis using seasonal autoregressive integrated moving-average (SARIMA) models.
Adults who acquired handguns between 2007 and 2016.
Excess handgun acquisitions (defined as the difference between actual and expected acquisitions) in the 6-week and 12-week periods after each shooting, overall and within subgroups of acquirers.
In the 6 weeks after the Newtown and San Bernardino shootings, there were 25 705 (95% prediction interval, 17 411 to 32 788) and 27 413 (prediction interval, 15 188 to 37 734) excess acquisitions, respectively, representing increases of 53% (95% CI, 30% to 80%) and 41% (CI, 19% to 68%) over expected volume. Large increases in acquisitions occurred among white and Hispanic persons, but not among black persons, and among persons with no record of having previously acquired a handgun. After the San Bernardino shootings, acquisition rates increased by 85% among residents of that city and adjacent neighborhoods, compared with 35% elsewhere in California.
The data relate to handguns in 1 state. The statistical analysis cannot establish causality.
Large increases in handgun acquisitions occurred after these 2 mass shootings. The spikes were short-lived and accounted for less than 10% of annual handgun acquisitions statewide. Further research should examine whether repeated shocks of this kind lead to substantial increases in the prevalence of firearm ownership.
Handgun acquisitions in California, 1 January 2007 to 25 February 2016.
Top. Number of handgun acquisitions per week in California. Bottom. Monthly rate of handgun acquisitions in California and of federal background checks for handgun acquisitions nationwide.
Table 1. Characteristics of Handgun Acquisitions and Acquirers in California in the 12 Months Before the Mass Shootings in Newtown and San Bernardino*
Actual and predicted weekly handgun acquisitions from 12 weeks before to 12 weeks after the mass shootings in Newtown (top) and San Bernardino (bottom).
Predicted acquisitions closely approximate actual acquisitions in most of the 12 weeks before the mass shootings, suggesting good model fit, except for the 5 weeks preceding the Newtown attack and the week preceding the San Bernardino attack. President Obama's reelection on 6 November 2012 and the Paris terrorist attacks on 13 November 2015 are probable explanations for these higher-than-expected acquisition rates in the preshooting periods (see Figures S8 and S9 in Supplement 4).
Table 2. Changes in Handgun Acquisitions in California in the 6 Weeks After the Mass Shootings in Newtown and San Bernardino, by Characteristics of Acquirers
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Studdert DM, Zhang Y, Rodden JA, Hyndman RJ, Wintemute GJ. Handgun Acquisitions in California After Two Mass Shootings. Ann Intern Med. ;166:698–706. doi: 10.7326/M16-1574
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Published: Ann Intern Med. 2017;166(10):698-706.
Published at www.annals.org on 2 May 2017
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