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Risk Factors and Risk Statistics for Sports Injuries

Hopkins, Will G PhD; Marshall, Stephen W PhD; Quarrie, Kenneth L; Hume, Patria A PhD

Clinical Journal of Sport Medicine: May 2007 - Volume 17 - Issue 3 - p 208-210
doi: 10.1097/JSM.0b013e3180592a68
Original Article: Original Research

Background: Risk factors for sports injuries include characteristics and behaviors of athletes and characteristics of sports and the environment that are associated with some measure of risk of injury.

Objective: To introduce risk statistics to clinicians evaluating studies of sports injuries.

Methods: Plain-language review of risk statistics and their practical application to sports injuries.

Results: The various measures of injury incidence are injury risk (proportion of athletes injured in a given period of training, playing, or other exposure time), injury rate (number of injuries per unit of exposure time), odds of injury (probability injury will happen divided by probability injury will not happen), injury hazard (instantaneous proportion injured per unit of time or mean injury count per unit of time), and mean time or mean number of playing exposures to injury. Effects of risk factors are estimated as values of effect statistics representing differences or ratios of one or more of these measures between groups defined by the risk factor. Values of some ratios and their sampling uncertainty (confidence limits) are estimated with specialized procedures: odds ratios with logistic regression, rate ratios with Poisson regression, and hazard ratios with proportional hazards (Cox) regression. Injury risks and mean time to injury in each group can also be estimated and can give a better sense of the effect of a risk factor. Risk factors identified in nonexperimental cohort and case-control studies are not always causes of injury; data from randomized controlled trials provide stronger evidence of causality.

Conclusion: Expressing risk statistics as meaningful numbers should help clinicians make better use of sports injury studies.

From the *Institute of Sport and Recreation Research NZ, AUT University, Auckland, New Zealand; †Injury Prevention Research Center, University of North Carolina, Chapel Hill, North Carolina; and ‡Research & Injury Prevention, New Zealand Rugby Union, Wellington, New Zealand.

Submitted for publication February 20, 2007; accepted March 6, 2007.

No sources of funding were provided for this paper.

Reprints: Will G. Hopkins, PhD, Institute of Sport and Recreation Research NZ, AUT University, Private Bag 92006, Auckland, NZ (e-mail:

Copyright © 2007 Wolters Kluwer Health, Inc. All rights reserved.