When The New York Times reports that 110 out of 111 NFL brains (99.09%) have chronic traumatic encephalopathy (CTE), everyone pays attention. Mothers worry about their kids. Some worry about their jobs. Senate subcommittees investigate. The Times article covers Dr. Ann McKee's recent article in the Journal of the American Medical Association, "Clinicopathological Evaluation of Chronic Traumatic Encephalopathy in Players of American Football" (JAMA. 2017;318(4):360-370) in dramatic fashion, illustrated with pathology slides of tissue samples from the brains of former football players and anecdotal information about them. Such claims are certain to be fuel for CTE litigation and cries to ban tackle football.
Let's put this in perspective. About 25,000 men have played American professional football. So, 110 is roughly 0.44%. Even if the real number is double, the outcome remains a statistical nonentity.
In all fairness, the study points out some of its limitations; for example, "Ascertainment bias associated with participation in this brain donation program." Inclusion was based entirely on exposure to repetitive head trauma eliminating any form of "control" group, a necessary element of any scientific study. The authors also disclose that "public awareness of a possible link" between head trauma and CTE "may have motivated" some participants. Finally, the authors acknowledge that the study is not representative of the population of all American football participants, as most play only at the youth or high school level, whereas the majority of the donors played at the professional level. The study data somewhat illustrates that point: CTE was found in none of two pre−high school participants and three of 14 high school participants (21%).
Breaking It Down
The 800-pound gorilla in this room is suicide. Suicide among former football players gets major media attention (Junior Seau and Aaron Hernandez) and has spawned a cottage industry of CTE litigation against every level of the sport from NFL down to Pop Warner. The study tries to correlate neuropathology with "clinical observations" − information drawn from "retrospective interviews" with family members of deceased donors. Observations are grouped as cognitive, behavioral or mood or both, and signs of dementia. Suicide was identified as the cause of death in 10% of the study group. "Suicidality" (ideation, attempts or completion) is identified among 33% of the study group. Some might conclude...