Reader Response: Association of Position Played and Career Duration and Chronic Traumatic Encephalopathy at Autopsy in Elite Football and Hockey Players
JesseMez, Associate Professor of Neurology, Boston University School of Medicine
Michael LAlosco, Associate Professor of Neurology, Boston University School of Medicine
Christopher JNowinski, Co-Founder & CEO, Concussion Legacy Foundation
Ann CMcKee, Professor of Neurology and Pathology, Boston University School of Medicine
YorghosTripodis, Associate Professor of Biostatistics, Boston University School of Public Health
Submitted February 27, 2021
Schwab et al.1 did not find a statistically significant association between position played and career duration and autopsy-confirmed chronic traumatic encephalopathy (CTE) in elite football and ice hockey players. The study’s limitations associated with statistical power, measurement error, and sample selection hinder interpretation of the presented data. The authors state that a sample size of about 14 is required “to detect a 50% difference in CTE diagnoses between groups with 80% power.”1 Player position is unlikely to account for a 50% difference in CTE status based on work by Mez et al., which indicates no effect for player position in >250 former football players.2 Assuming that player position accounts for a much smaller effect in CTE status, such as 10%, a sample size of approximately 400 would be needed. In Mez et al., each additional year of football play accounted for a 30% increase in odds of CTE.2 Given the sample size and standard deviation reported for career duration in this manuscript, the authors were only 80% powered to detect an effect 2.4 times larger and were only 55% powered to detect the effect presented in Mez et al.
Additionally, career duration was problematically measured. The authors state that “age of retirement was used as an indicator of overall career duration.”1 However, two elite athletes can retire at the same age, but have very different career lengths—specifically in football, where players begin tackling as early as age four and as late as age 20.3 Furthermore, the authors equate football players with ice hockey players, which are two sports with very different repetitive head impact (RHI) exposure profiles.4 Given these concerns with statistical power and appropriate measurement of RHI exposure, we question the validity of the reported results.
Disclosure
The author reports no relevant disclosures. Contact journal@neurology.org for full disclosures.
References
Schwab N, Wennberg R, Grenier K, Tartaglia C, Tator C, Hazrati LN. Association of Position Played and Career Duration and Chronic Traumatic Encephalopathy at Autopsy in Elite Football and Hockey Players [published online ahead of print, 2021 Feb 24]. Neurology. 2021;10.1212/WNL.0000000000011668. doi:10.1212/WNL.0000000000011668
Mez J, Daneshvar DH, Abdolmohammadi B, et al. Duration of American Football Play and Chronic Traumatic Encephalopathy. Ann Neurol. 2020;87(1):116-131. doi:10.1002/ana.25611
Alosco ML, Mez J, Tripodis Y, et al. Age of first exposure to tackle football and chronic traumatic encephalopathy. Ann Neurol. 2018;83(5):886-901. doi:10.1002/ana.25245
Schwab et al.1 did not find a statistically significant association between position played and career duration and autopsy-confirmed chronic traumatic encephalopathy (CTE) in elite football and ice hockey players. The study’s limitations associated with statistical power, measurement error, and sample selection hinder interpretation of the presented data. The authors state that a sample size of about 14 is required “to detect a 50% difference in CTE diagnoses between groups with 80% power.”1 Player position is unlikely to account for a 50% difference in CTE status based on work by Mez et al., which indicates no effect for player position in >250 former football players.2 Assuming that player position accounts for a much smaller effect in CTE status, such as 10%, a sample size of approximately 400 would be needed. In Mez et al., each additional year of football play accounted for a 30% increase in odds of CTE.2 Given the sample size and standard deviation reported for career duration in this manuscript, the authors were only 80% powered to detect an effect 2.4 times larger and were only 55% powered to detect the effect presented in Mez et al.
Additionally, career duration was problematically measured. The authors state that “age of retirement was used as an indicator of overall career duration.”1 However, two elite athletes can retire at the same age, but have very different career lengths—specifically in football, where players begin tackling as early as age four and as late as age 20.3 Furthermore, the authors equate football players with ice hockey players, which are two sports with very different repetitive head impact (RHI) exposure profiles.4 Given these concerns with statistical power and appropriate measurement of RHI exposure, we question the validity of the reported results.
Disclosure
The author reports no relevant disclosures. Contact journal@neurology.org for full disclosures.
References