What happened: Researchers identified every former player who appeared in at least one NFL game and died from 2016 through 2021. Postmortem exams confirmed CTE in 215 of the 235 brains evaluated.
Why it matters: The population-based design establishes a lower bound while reducing the selection bias that has limited brain-bank studies. CTE is linked to repeated head impacts and can be definitively diagnosed only after death.
By the numbers: Of 878 deaths, 235 brains were examined and 215 had CTE. That is 91.5% among examined brains and 24.5% across the full cohort, making one in four a minimum estimate.
What to watch: Broader brain donation and better tools for studying living former players could help narrow the true prevalence range.