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Research Christmas 2017: Natural Phenomena

The full moon and motorcycle related mortality: population based double control study

BMJ 2017; 359 doi: (Published 11 December 2017) Cite this as: BMJ 2017;359:j5367
  1. Donald A Redelmeier, professor of medicine1,
  2. Eldar Shafir, professor of psychology and public affairs2
  1. 1Department of Medicine, University of Toronto, Canada; Division of General Internal Medicine, Sunnybrook Health Sciences Centre, Toronto, ON M4N 3M5, Canada
  2. 2Department of Psychology, Princeton University, NJ, USA; Woodrow Wilson School of Public and International Affairs, Princeton University, NJ, USA
  1. Correspondence to: D A Redelmeier dar{at}
  • Accepted 1 November 2017


Objective To test whether a full moon contributes to motorcycle related deaths.

Design Population based, individual level, double control, cross sectional analysis.

Setting Nighttime (4 pm to 8 am), United States.

Participants 13 029 motorcycle fatalities throughout the United States, 1975 to 2014 (40 years).

Main outcome measure Motorcycle fatalities during a full moon.

Results 13 029 motorcyclists were in fatal crashes during 1482 relevant nights. The typical motorcyclist was a middle aged man (mean age 32 years) riding a street motorcycle with a large engine in a rural location who experienced a head-on frontal impact and was not wearing a helmet. 4494 fatal crashes occurred on the 494 nights with a full moon (9.10/night) and 8535 on the 988 control nights without a full moon (8.64/night). Comparisons yielded a relative risk of 1.05 associated with the full moon (95% confidence interval 1.02 to 1.09, P=0.005), a conditional odds ratio of 1.26 (95% confidence interval 1.17 to 1.37, P<0.001), and an absolute increase of 226 additional deaths over the study interval. The increase extended to diverse types of motorcyclists, vehicles, and crashes; was accentuated during a supermoon; and replicated in analyses from the United Kingdom, Canada, and Australia.

Conclusion The full moon is associated with an increased risk of fatal motorcycle crashes, although potential confounders cannot be excluded. An awareness of the risk might encourage motorcyclists to ride with extra care during a full moon and, more generally, to appreciate the power of seemingly minor distractions at all times.


  • Contributors: DAR wrote the first draft of the manuscript. Both authors contributed to the study design, manuscript preparation, data analysis, results interpretation, critical revisions, and final decision to submit. DAR had full access to all the data in the study, takes responsibility for the integrity of the data, and is accountable for the accuracy of the analysis. DAR is the guarantor.

  • Funding: This project was supported by a Canada research chair in medical decision sciences, the Canadian Institute for Advanced Research, the Canadian Institutes of Health Research, and the Ontario Ministry of Transportation. The views are those of the authors and do not necessarily reflect the Ontario Ministry of Health.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The study protocol was approved by the research ethics board of Sunnybrook Health Sciences Center, including a waiver for direct patient consent. All data are available through the National Highway Traffic Safety Agency.

  • Data sharing: No additional data are available. Original data are available at the National Highway Traffic Safety Administration Fatality Analysis Reporting System (

  • Transparency: The lead author (DAR) is the manuscript’s guarantor and affirms the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

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