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Comment & Response
February 4, 2019

Association Between April 20 Cannabis Celebration and Fatal Crashes

Author Affiliations
  • 1Department of Medicine, University of British Columbia, Vancouver, British Columbia, Canada
  • 2Centre for Clinical Epidemiology and Evaluation, Vancouver, British Columbia, Canada
  • 3Centre for Health Evaluation and Outcome Sciences, Vancouver, British Columbia, Canada
  • 4Department of Medicine, University of Toronto, Toronto, Ontario, Canada
  • 5Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada
JAMA Intern Med. 2019;179(3):456. doi:10.1001/jamainternmed.2018.8094

To the Editor In our Research Letter1 examining crash risks on the “4/20” counterculture holiday, we identified drivers (rather than crashes) as the unit of analysis because one or more drivers may contribute to a crash. This approach also helps optimize interpretability for clinicians and policymakers around driving risks despite breaching strict assumptions for statistical independence. Furthermore, as Aydelotte and colleagues2 point out, similar results were obtained whether the driver (OR, 1.12; 95% CI, 1.05-1.19) or the crash (incidence rate ratio, 1.10; 95% CI, 1.02-1.20) was the unit of analysis. The observed difference in calculated absolute risks simply indicates the average crash involves more than one driver.

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