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What proportion of athletes sustained an injury during a prospective study? Censored observations matter
  1. Jonatan Jungmalm1,
  2. Michael Lejbach Bertelsen2,
  3. Rasmus Oestergaard Nielsen2
  1. 1Department of Food and Nutrition and Sport Science, Center for Health and Performance, University of Gothenburg, Goteborg, Sweden
  2. 2Department of Public Health, Section for Sport Science, Aarhus University, Aarhus, Denmark
  1. Correspondence to Mr Jonatan Jungmalm, Center for Health and Performance, Department of Food and Nutrition, and Sport Science, University of Gothenburg, Goteborg, Sweden; jonatan.jungmalm{at}gu.se

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Introduction

A common question in sports injury research is ‘what proportion of athletes sustained an injury over a certain time period?’. In cross-sectional studies, where data are collected at a single point in time, the prevalence proportion is simply the number of injured athletes divided by the total sample. In prospective cohort studies, caution is needed as the injury incidence proportion (proportion of newly injured athletes during the observation period) is likely to be underestimated by simply using the approach that is valid for cross-sectional studies. As a part of the BJSM methods matter series,1 we here compare the analytical approaches for cross-sectional studies and prospective cohort studies (ie, without censoring and with censoring, respectively) to help the reader accurately estimate incidence proportion in prospective studies.

Cumulative incidence proportion (CIP)

To describe the proportion of sports injuries occurring over a given time period, one can calculate the CIP. The CIP can be calculated with or without censoring (in this paper, we discuss the concept of ‘right censoring’, but use the term ‘censoring’ only). For instance, the number of injured runners in a 1-year prospective cohort study was 252 of 931.2 Hence, the CIP calculated without censoring is 27% …

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