The 25% CTE figure rests on 338 donated brains out of 1,712 NFL deaths
The BMJ study's range runs from 24.5% to 97.7% because 1,374 of those brains were never examined. That width reflects who donates, not how common the disease is.
The Scientist · Science desk
What happened
- A study published Aug. 25 in The BMJ examined donated brain tissue from 338 former NFL players who died between 2008 and 2021.
- Some 1,712 former players died over that same period, so the pathologists saw roughly one in five of the brains that could in principle have been examined.
- Over 93% of the donated brains carried the accumulations of abnormal protein in specific tissue locations that are used to diagnose CTE.
- Extrapolating from that subset, the researchers put CTE prevalence between 24.5% and 97.7% for deaths from 2016 to 2021, the window they judged their most representative.
- The authors caution that their findings cannot necessarily be generalized to the American football community.
Why it matters
- What it limits constraint A range 73 points wide reflects the recruitment method itself, so practitioners waiting for a firmer prevalence number need a differently recruited brain bank rather than more statistical analysis.
- What doesn't add up contradiction Munce reads the paper as a historical document with little to say about current play, while the players' union treats it as grounds for action across all of football, and both readings sit on the same 338 brains.
- Who has to decide decision Anyone setting youth or college policy has to decide whether an interval this wide is actionable, and the Stat News historian argues the pre-existing evidence already settles that question without it.
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Work the lower bound backwards and you can see how it was built. Multiply 18.5% by the 1,712 deaths and you get roughly 317 brains, which is about 94% of the 338 examined [22] - the same pathology rate the authors reported among their donors [6]. The floor is that count of confirmed cases divided by every death in the era, on the assumption that all 1,374 brains never donated were free of disease [21].
Run the assumption the other way and the ceiling appears: 317 confirmed plus 1,374 assumed, over 1,712 deaths, is 98.8%, within rounding of the 98.7% the paper published for the full window [23] [10]. The 24.5% to 97.7% band for 2016 to 2021 is the same construction on a smaller slice, and it is 73 percentage points wide [19] [1]. Closing that gap depends on recruiting differently, for instance through a route that does not rely on families noticing symptoms; statistical refinement alone will not do it. Thayne Munce of the University of Kansas, who was not involved in the work, put the mechanism plainly: if the men who donated were largely those showing cognitive or behavioural changes while alive, the sample is heavily biased, and the width of the range is what that bias looks like when written down [13].
The pathology count and the impairment count are also different measurements. CTE is a degenerative disease attributed to repeated concussions and smaller non-concussive hits [3], and it was scored here in tissue: about 60% of donors with CTE-related changes also had a dementia diagnosis, so around 40% did not, though stage IV cases reached 90% [8] [24] [9]. About 30% of the donated brains were stage IV [7].
Then there is the calendar. Men who died between 2008 and 2021 did their playing in earlier decades, which is why Munce says the findings should not be pushed onto youth players or onto today's NFL, and why he offers the view that this is probably the safest time to be playing the sport [11] [12]. That is a statement about direction with no denominator attached, and worth reading as exactly that.
The Stat News historian objects to a different part of the coverage, and the objection is not about the arithmetic. Earlier studies had estimated similar prevalence among professional players, and a 1933 NCAA medical handbook already described concussion producing "punch drunk" [18] [17]. On that reading the new number re-quantifies a known problem, and safety decisions at the college and youth levels do not need the interval to shrink first [16]. The authors themselves call 25% the low end [2]. My own read: carry the 338-of-1,712 ratio [20] into any argument about this paper, and treat 25% as a floor for men whose careers are already over.
What to watch
- Any follow-up that ascertains CTE status through something other than family-initiated donation, which is the only route to a narrower interval.
- Whether the NFL Players Association's call to action produces a named rule or practice change at the youth and college levels.
- A prevalence estimate drawn from a more recent playing era, which is the only kind that would test Munce's claim about current players.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence60
- Adoption
- Not scored
- Hype gap+10
- Incentives
- Not scored
- Confidence60
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
For 2016 to 2021, the period with the highest number of brain donations, the researchers estimated the CTE rate at between 24.5% and 97.7%, and determined that window was likely the more representative sample.
- [2]
The study's authors have suggested the roughly 25% estimate is on the low end, with maximum possible prevalence around 98%.
- [3]
CTE is a degenerative brain disease caused by repeated concussions and smaller non-concussive hits.
- [4]
A study published Aug. 25 in The BMJ examined donated brain tissue from 338 former NFL players who died between 2008 and 2021.
- [5]
A total of 1,712 former NFL players died in that time frame, so the analysis included only about 20% of the brains that could theoretically have been examined.
- [6]
Among the donated brains, over 93% showed physical signs of CTE, meaning an accumulation of abnormal proteins in specific places within the tissue.
- [7]
About 30% of the donated brains had stage IV CTE, the most severe form.
- [8]
Only about 60% of the individuals with CTE-related brain changes were also diagnosed with dementia in the study.
- [9]
Those with stage IV CTE were more likely to have dementia, with 90% having a diagnosis.
- [10]
Across the full study time frame, the researchers estimated that between 18.5% and 98.7% of the deceased players likely had CTE.
- [11]
Thayne Munce, an associate professor and director of the Jayhawk Athletic Performance Laboratory at the University of Kansas, who was not involved in the BMJ study, cautioned that its findings should not be extrapolated to all levels and ages of play, or even to today's NFL players.
- [12]
Munce is quoted saying that this is probably the safest time to be playing the sport of football.
- [13]
Munce said that if the majority of players who donated their brains were those showing outward signs of dementia, cognitive decline or behavioural changes while living, the sample becomes highly biased, and that is where the wide range of estimates comes from.
- [14]
The authors note that the findings cannot necessarily be generalized to the American football community.
- [15]
In a statement reported by ESPN, the NFL Players Association said the findings should serve as a call to action across the entire football ecosystem.
- [16]
The Stat News author, a historian of science who has studied the history of traumatic brain injury in football, argues the statistic re-quantifies but does not reveal a problem, and that action to make other sports and the college and youth levels of football safer need not wait for that level of scientific evidence.
- [17]
A 1933 NCAA Medical Handbook for Schools and Colleges acknowledged that concussion caused punch drunk, what would now be called CTE.
- [18]
Earlier studies have estimated similar prevalence of CTE among professional football players.
- [19]
The 2016 to 2021 estimate spans 73.2 percentage points.
- [20]
The 338 examined brains are 19.7% of the 1,712 former players who died in the study window.
- [21]
1,374 of the deceased players' brains were never donated or examined.
- [22]
The published 18.5% floor corresponds to about 317 CTE-positive donors, which is about 93.8% of the 338 brains examined, matching the reported donor pathology rate.
- [23]
Treating all 1,374 unexamined brains as CTE cases alongside the roughly 317 confirmed ones gives 98.8% of the 1,712 deaths, within rounding of the published 98.7% upper bound.
- [24]
About 40% of donors with CTE-related brain changes did not have a dementia diagnosis.
Sources
2 independent publishers whose own reporting we read for this story.
- livescience.com'This is probably the safest time to be playing the sport of football': Concussion expert explains why viral CTE study may not be as scary as it sounds
2 articles · September 1, 2026
- statnews.comOpinion: The most shocking thing about the latest statistics on CTE in football is that we find them so shocking
1 article · August 31, 2026
Topics and entities
Topics
- Sports concussion
- Chronic traumatic encephalopathy
Entities
- University of Kansas
- NFL Players Association
- NCAA
- National Football League