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CTE 36 SEP / OCT 2023 I  HEALTHCARE JOURNAL OF ARKANSAS dichotomous CTE outcomes. The bootstrap approach was used to evaluate differences in discriminative power between mod- els 70 . To further evaluate predictive ability of each model, a 10-fold cross-validation study was performed for each significant exposure measure and both dichotomous CTE outcomes. We fitted linear regressions to quantify the association of each exposure measure with NFT burden, a semi quantitative mea- sure consisting of a zero to three score for each region, summed across 11 brain regions (total range: 0–33). These analyses were restricted to data from athletes with all 11 brain regions available for neuropathologi- cal evaluation (82.1%). Imputation was not performed for missing brain region data because we were sufficiently powered with- out imputation. Additionally, missingness was not associated with exposure measures after adjusting for age at death, so estimated effects were unlikely to be biased by differ- ential missingness. All models were adjusted for age at death given its known association with CTE pathology. For all models, Bayesian infor- mation criterion (BIC) was calculated to aid in comparison of model fits. To adjust for multiple analyses, the Bonferroni-adjusted significance level of 0.0083 was used. All data were collected and secured using Bos- ton University Medical Center REDCap. All analyses were performed with R v4.0.5 or SPSS v.27.0.1.0. Given the high-profile and sensitive information for these donors, access to data is strictly monitored to ensure confidentiality. Deidentified biospecimens and limited dataset clinical are available upon submission of IRB approved proposal and data use agreement. Please contact cor- responding author to initiate this process. All code is available upon request to the cor- responding author. Reporting summary Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article. n DATA AVAILABILITY The raw datasets generated during and/or analyzed during the current study are not publicly available due to potential ability to identify elite athletes based on exposure data. However, these data are available from the corresponding author on request and with relevant IRB approval. Source data are provided with this paper. REFERENCES 1 Mez, J. et al. Clinicopathological Evaluation of Chron- ic Traumatic Encephalopathy in Players of American Football. JAMA 318, 360–370 (2017). 2 Mckee, A. C. & Daneshvar, D. H. The neuropathol- ogy of traumatic brain injury. Handb. Clin. Neurol. 127, 45–66 (2015). 3 Bieniek, K. F. et al. The Second NINDS/NIBIB Con- sensus Meeting to Define Neuropathological Criteria for the Diagnosis of Chronic Traumatic Encephalopa- thy. J. Neuropathol. Exp. Neurol. 80, 210–219 (2021). 4 McKee, A. C. et al. The spectrum of disease in chron- ic traumatic encephalopathy. Brain 136, 43–64 (2013). 5 Mez, J. et al. Duration of American Football Play and Chronic Traumatic Encephalopathy. Ann. Neurol. 87, 116–131 (2020). 6 Robbins, C. A. et al. Self-reported concussion his- tory: impact of providing a definition of concussion. Open Access J. Sports Med 5, 99–103 (2014). 7 Lessley, D. J. et al. Position-Specific Circumstances of Concussions in the NFL: Toward the Development of Position-Specific Helmets. Ann. Biomed. Eng. 48, 2542–2554 (2020). 8 Cobb, B. R., Rowson, S. & Duma, S. M. Age-related differences in head impact exposure of 9–13 year old football players. Biomed. Sci. Instrum. 50, 285–290 (2014). 9 Cobb, B. R. et al. Head impact exposure in youth football: elementary school ages 9–12 years and the effect of practice structure. Ann. Biomed. Eng. 41, 2463–2473 (2013). 10 Bellamkonda, S. et al. Head Impact Exposure in Practices Correlates With Exposure in Games for Youth Football Players. J. Appl Biomech. 34, 354–360 (2018). 11 Campolettano, E. T., Rowson, S. & Duma, S. M. Drill- specific head impact exposure in youth football prac- tice. J. Neurosurg. Pediatr. 18, 536–541 (2016). 12 Daniel, R. W., Rowson, S. & Duma, S. M. Head im- pact exposure in youth football. Ann. Biomed. Eng. 40, 976–981 (2012). 13 Daniel, R. W., Rowson, S. & Duma, S. M. Head ac- celeration measurements in middle school football. Biomed. Sci. Instrum. 50, 291–296 (2014). 14 Gellner, R. A., Campolettano, E. T., Smith, E. P. & Rowson, S. Are specific players more likely to be involved in high-magnitude head impacts in youth football? J. Neurosurg. Pediatr. 24, 47–53 (2019). 15 Kelley, M. E. et al. Head Impact Exposure in Youth Football: Comparing Age- and Weight-Based Levels of Play. J. Neurotrauma 34, 1939–1947 (2017). 16 Kelley, M. E. et al. Physical Performance Measures Correlate with Head Impact Exposure in Youth Foot- If you played college or pro football and would like to donate your brain for this important CTE research, please go to ConcussionFoundation. org/get-involved/research-registry. For urgent brain donation matters, please call the Boston University CTE Center's 24/7 voicemail/ pager at 617-992-0615. For general brain donation inquiries, please contact: Evan Nair by phone at 617-358-5996 or Madeline Uretsky by phone at 617-358-6027. Brain donation must be made soon after death. BU has extensive networks across the country and coordinates the donation at no charge to the families of current and former college and pro players whether or not CTE is suspected.