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Mortality of Japanese Olympic athletes: 1952–2017 cohort study
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  • Published on:
    Longer career, longer follow up, immortality bias
    • Juliana Antero, Researcher The French National Sports Institute (INSEP)
    • Other Contributors:
      • Aurélien Latouche, Professor
      • Jean-François Toussaint, Professor

    The article Mortality of Japanese Olympic athletes: 1952 – 2017 cohort study currently fails to account for a probable source of non-negligible bias. Whilst the main finding, stating that there is a decreased mortality rate among Japanese Olympians appears to be methodologically reliable, the authors also state that “higher mortality was observed among those who participated in the Olympics twice and three times or more compared with those who participated just once,” which we believe to be a potentially inaccurate finding.
    A delayed entry exists at baseline, as those with longer careers tend to be older than those with shorter careers. For instance, someone who has participated in 3 Olympic Games started her/his Olympic career 12 years before those who have participated only once. Thus, there might be an important period effect underlying these findings. Even if the authors have adjusted the analysis by age, this is not equivalent to adjusting for period, as earlier periods in time are related with higher mortality rates, which could explain the findings.
    Additionally, another problem often seen in survival studies is ignoring when a death event occurs. This is problematic because deaths will be observed more frequently in subjects with longer follow-up times. In the presence of time-dependent bias, the hazard ratio is artificially underestimated and the length bias leads to an artificial underestimation of the overall hazard [2]. Therefore, faulty interpretat...

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    Conflict of Interest:
    None declared.