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Risk of Injury Due to Alcohol: Evaluating Potential Bias Using the Case-Crossover Usual-Frequency Method

Ye, Yu; Bond, Jason; Cherpitel, Cheryl J.; Stockwell, Tim; Macdonald, Scott; Rehm, Jürgen

doi: 10.1097/EDE.0b013e3182801cb4

Background: The usual-frequency case-crossover method, comparing exposure before an event with typical exposure of the same person, is widely used to estimate the risk of injury related to acute alcohol use. Prior results suggest that risk estimates might be biased upward compared with other methods.

Methods: Using data from 15 emergency room studies in seven countries, we compared the usual-frequency case-crossover method with case-control analysis, using noninjury patients as controls. Control-crossover analysis was performed to examine potential bias and to adjust risk estimates.

Results: The cross-study pooled odds ratio (OR) of injury related to drinking was 4.7 (95% confidence interval = 2.6–8.5) in case-crossover analysis and 2.1 (1.6–2.7) in case-control analysis. A control-crossover analysis found an indication of bias (OR = 2.2 [1.8–2.8]), which was larger among less-frequent drinkers.

Conclusion: Findings suggest that the potential overestimation of injury risk based on the usual-frequency case-crossover method might be best explained by recall bias in usual-frequency estimates.

aAlcohol Research Group, Public Health Institute, Emeryville, CA; bCenter for Addictions Research of BC and Department of Psychology, University of Victoria, Victoria, BC, Canada; cCenter for Addictions Research of BC and School of Health Information Science, University of Victoria, Victoria, BC, Canada; dCentre for Addiction and Mental Health and Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada; and eEpidemiological Research Unit, Technische Universität Dresden, Klinische Psychologie and Psychotherapie, Dresden, Germany.

Submitted 19 December 2011; accepted 27 November 2012.

Supported by grants from the U.S. National Institute on Alcohol Abuse and Alcoholism R01 AA013750 and P50 AA005595.

The authors report no conflict of interest.

Correspondence: Yu Ye, 6475 Christie Avenue Suite 400, Emeryvile, CA 94608. E-mail:

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