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Abbreviations: AFE, age of first exposure; IQR, interquartile range.
Independent sample t-tests and χ2-analyses were used to compare differences between the AFE groups, except for seasons of football play, total number of concussions and total number of concussions outside of sport/military for which Mann–Whitney U-test was conducted due to a non-normal distribution. Proportion of white versus other was tested and the highest level of football play was transformed to amateur versus professional.
aIncludes reported history of depression, anxiety, bipolar disorder, schizophrenia and/or other psychiatric difficulties.
bSelf-reported number of concussions after being provided with a modern definition of concussion.62
cOnly 39 (18.2%) subjects reported a military history, and the median number of head injuries experienced during the military was 0 (IQR=1).
dPlayers could indicate both a primary offensive and defensive position and therefore could be represented more than once. The bold is used for those P values that are significant.