Commentary: The Injury Proportion Ratio: What's It All About?

Abstract

We thank the Journal of Athletic Training (JAT ) and Deits et al1 for allowing us to comment on the analysis of national emergency department (ED) surveillance data on hockey injuries appearing in this issue. This commentary focuses on the use in descriptive epidemiology of the injury proportion ratio (IPR). We are prompted to comment on the IPR due to its increasing use in the sports injuryprevention literature, including JAT. Our comments are aimed at examining the IPR and highlighting the usefulness and limitations of the measure in relation to other measures in injury-prevention research, notably the injury rate ratio. Our concern is that, without understanding the assumptions underlying these measures, the IPR can be easily misinterpreted, thereby leading readers to draw false conclusions. Published research2–6 has used IPRs in the context of hospital-based surveillance data as well as a Web-based high school surveillance system.7–16 By design, hospitalbased ED injury surveillance systems, such as the National Electronic Injury Surveillance System (NEISS), collect information only on injured individuals. Such surveillance systems provide useful descriptive information about severe injury patterns, such as who was injured, what types of injuries occurred, what was happening at the time of injury, and the type of care provided for that injury. However, NEISS does not collect information about the population among whom these injuries occurred or arose: the population of hockey players, in this case. Additionally, NEISS does not collect information on hockey injuries that do not result in a visit to the ED, an issue we will ignore for the purposes of this commentary.