Boston University researchers estimated that 74.5% of former NFL players who died between 2008 and 2023 had chronic traumatic encephalopathy after they tried to correct for who donates brains, according to a study in JAMA Network Open described by CBS News and ABC News on Wednesday^1,2.

CTE is a degenerative brain disease linked to repeated head blows and can be diagnosed only after death^1,2. ABC News said the team looked at 2,362 deceased former NFL players, including 396 who donated brains and 1,966 who did not².

Among donors, CTE was found in about 93.5% to 94% of brains, the two reports said, with CBS citing 362 of 387 donors^1,2. Families of players with cognitive symptoms were about five times more likely to donate, Boston University said, and that ratio was used to bring the donor figure down to 74.5%¹. Co-author Yorghos Tripodis told ABC News that even under very conservative assumptions the estimate does not go below 60%².

The paper also estimated that about one in four former NFL players had dementia in life, ABC News reported². CBS said the authors stressed the work covers players who have died and does not predict how many living former or active players have CTE¹.

The findings tighten an August study by overlapping authors that put possible CTE among players who died from 2016 to 2021 somewhere between 25% and 98%, both outlets said^1,2. "Our group's earlier study could only say the figure was somewhere between 25% and 98%," Tripodis told ABC News².

Lead author Julia Gallini said in a Boston University statement that CTE is found in less than 1% of donors to community brain banks, CBS reported¹. Researchers note families who saw cognitive symptoms may be more likely to donate, which can inflate unadjusted rates².

The NFL said it continuously strives to make football safer, including strategies to reduce concussions and head impacts, and pointed to equipment and rule changes, CBS reported¹. The NFL Players Association told CBS the study is among work that is critical to understanding football's long-term health effects and said it remains committed to research and care¹. ABC News said it had asked the NFL for comment on the new JAMA paper².

The estimate depends on statistical correction for donation bias and on autopsy diagnoses; how well that maps onto living players, and how often CTE pathology produces symptoms, is not settled in these reports^1,2. Not medical advice.