Variation in injury incidence rate reporting

Background: Injury incidence rates are commonly reported using either a time-based denominator, such as injuries per 1000 player hours, or an event-based denominator, such as injuries per 1000 athletic exposures. Unless researchers give very detailed baseline information on their study population, it is not possible to convert between these units. We previously observed an apparent geographic split in reporting injury incidence rates between American and non-American researchers. Methods: We manually searched all issues of The American Journal of Sports Medicine and British Journal of Sports Medicine published between January 1, 2009 and December 31, 2013 for studies reporting injury risk or incidence during organized sporting events. For each article, the following information was recorded: journal, geographic location of the senior author, method of injury reporting (risk or incidence), incidence rate reporting method (time-based vs. event-based), sports studied, event types included (practice, game/match, or both), injury types reported. Results: A total of 109 articles that reported injury risk or rate were identified. Seventy-four articles reported injury incidence. Twenty-five of the 74 articles reporting injury incidence were written by American researchers, and 92% of these utilized an event-based denominator. Forty-five of the 49 (92%) articles reporting injury incidence written by non-American authors utilized a time-based denominator. Conclusions: Over the last five years, American researchers have chosen to report rates in terms of injuries per athletic exposure, while non-American researchers have preferred time-based rate reporting. Standardization of reporting measures would facilitate cross-sport comparisons of injury rates and metaanalyses of existing studies.