One in four is a floor, not a finding: CTE research finally gets a denominator
The new BMJ cohort counts confirmed cases against every NFL decedent, which makes 25% arithmetic and everything above it argument. That distinction is what liability models will run on.
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What happened
- Researchers built a roster of every man to play an NFL game since 1949 and used CDC death records to identify 1,712 who died between 2008 and 2021.
- At least a quarter of those decedents had CTE at death, with the paper's own bounding analysis reaching as high as about 97 percent.
- Among the more than 330 brains donated across the full period, 93 percent showed the pathology.
- A secondary analysis found dementia in over 90 percent of stage IV cases and in roughly 40 percent of donors with no CTE at all.
Why it matters
- What it costs cost A bounded population rate is something an insurer or a plaintiff's actuary can reserve against, and reserves in a contact-sport business are funded out of current payroll and premiums rather than...
- What it limits constraint Because the donors died at a mean age of 66 with careers largely ending before 2005, neither the league nor its critics can honestly use this figure to argue about the current rulebook.
- Who's exposed exposure The same paper hands defendants their causation wedge: an employer can accept the pathology rate and still contest that tau explains any particular man's decline.
- What it sets up precedent If OSHA's inherent-and-inseparable exclusion is finalised, occupational-hazard arithmetic about paid physical performance stops being a regulatory matter and becomes purely a tort one.
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The quarter is not an estimate. Of the 878 former NFL players who died between 2016 and 2021, the investigators had pathology on 235, about 27 percent of the cohort [3][22]. Vox's newsletter account puts the in-window examined count at 235; the full-period donation total reported elsewhere is 338, at a 93 percent positivity rate [c6b][4]. Apply that rate to the in-window subset and you get roughly 219 confirmed cases, or 24.9 percent of everyone who died in those six years [11]. The headline figure is confirmed disease divided by all decedents, which is why it behaves like a floor rather than a central estimate.
Everything contested sits in the 643 brains nobody examined [23]. The paper's own bound runs to about 97 percent if every non-donor except the 20 definitively cleared brains had the disease [1]; the authors allow that the real rate may be near 90 percent [24]; the 2019 Binney and Bachynski modelling exercise put it closer to 10 percent [12]. Donation is symptom-driven and non-random [6], so the ceiling is as much an artifact of who volunteers as the floor is of who does not.
For anyone pricing physical risk, the floor is the usable number precisely because selection bias cannot inflate a count. It sits over a near-complete roster of every man to play a game since 1949 and a national vital-statistics denominator [8], and it is conservative in a specific way: another 215 non-donors had a neurodegenerative disease listed on the death certificate, on a document type that undercaptures those diagnoses [14].
The defence material is in the same paper. Dementia showed up in more than 90 percent of stage IV cases, but also in roughly 40 percent of donors whose brains were clear of CTE, with weak correlation at lower stages [10]. Uzma Samadani, a neurosurgeon who consulted for the NFL from 2015 to 2019, warns against repeating the amyloid hypothesis and treating mislocalized tau as proven cause of symptoms [16]. A defendant can concede a 25 percent pathology rate and still contest causation in any individual case.
Then there is vintage. Mean age at death among donors was about 66, so most careers ended before 2005, ahead of helmet grading, kickoff redesign, targeting enforcement and contact-practice limits [15]. Vox's newsletter reaches for black lung as the analogy [18], but black lung came with an exposure standard; the closest regulatory move here runs the other way, OSHA having proposed excluding hazards inherent and inseparable from the core nature of a professional activity, a proposal not yet finalised [17]. Meanwhile the labour supply thins while demand does not: tackle participation among 13-to-17-year-olds fell 9 percent from 2019 to 2024 and now trails tennis [19], while NFL games were 83 of last year's 100 top-rated television programmes [21].
Both the league and the plaintiffs' bar can quote this study accurately and land in opposite places, because a 72-point interval is wide enough to hold both readings [13].
What to watch
- Whether OSHA finalises the inherent and inseparable exclusion, and whether its text reaches professional sport explicitly.
- Whether donation rates in later cohorts rise enough to narrow the gap between the 25 percent floor and the 97 percent ceiling.
- Whether anyone assembles a cohort restricted to careers that began after helmet grading, kickoff redesign and contact-practice limits.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence74
- Adoption58
- Hype gap+18
- Incentives62
- Confidence71
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
Placed over the population denominator, the donor findings yield a minimum prevalence at death of roughly 25% for the 2016-2021 cohort, with a theoretical ceiling of about 97% assuming every non-donor had the disease except the 20 brains definitively cleared.
- [2]
A retrospective population-based cohort was published in The BMJ by Daneshvar and colleagues at Mass General Brigham, Boston University and the Concussion & CTE Foundation.
- [3]
The study examined the brains of 235 of the 878 former NFL players who died between 2016 and 2021.
- [4]
Among the more than 330 NFL brains donated across the full period, 93% showed CTE.
- [5]
Among the 338 players whose brains were donated and studied, the CTE rate was 93%.
- [6]
Brain donation is symptom-driven and non-random, which inflates any brain-bank numerator, and the resulting 25%-97% interval is honest but not clinically accurate for counselling any individual player.
- [7]
CTE research has had a denominator problem: the 2017 JAMA series reporting CTE in 110 of 111 donated NFL brains was a numerator in search of a population, and was repeatedly misreported as a prevalence figure.
- [8]
Investigators assembled a roster of every man who appeared in at least one NFL game since 1949 and used CDC death-certificate data to identify 1,712 who died between 2008 and 2021.
- [9]
The analytic window was narrowed to 2016-2021, when the proportion of decedents whose brains reached the UNITE Brain Bank was highest.
- [10]
More than 90% of stage IV CTE cases carried a clinician-assigned dementia diagnosis, but roughly 40% of donors whose brains were free of CTE also had dementia, and the correlation at lower pathologic stages was weak.
- [11]
Applying the 93% donor positivity rate to the 235 examined brains gives roughly 219 confirmed cases, or 24.9% of all 878 decedents, which reproduces the reported 25% floor.
- [12]
The study is the empirical successor to the modelling exercise Binney and Bachynski published in 2019, which placed the denominator closer to 10%.
- [13]
The published bound spans 72 percentage points.
- [14]
An additional 215 non-donors had a neurodegenerative disease listed on the death certificate, and certificates systematically undercapture those diagnoses.
- [15]
Mean age at death among donors was roughly 66 years, meaning most careers ended before 2005, before helmet grading, kickoff redesign, targeting enforcement or contact-practice limits; prevalence at death is not lifetime risk.
- [16]
Uzma Samadani, MD, PhD, a neurosurgeon who consulted for the NFL from 2015-2019 and founded Oculogica, cautioned that association does not imply causation, citing the long dominance of the amyloid hypothesis in Alzheimer's, and said it is not yet proven that hyperphosphorylated mislocalized tau causes symptoms of encephalopathy.
- [17]
The Trump administration advanced an OSHA proposal to formally exclude from standards enforcement hazards that are inherent and inseparable from the core nature of a professional activity; the proposal has not been finalised.
- [18]
Vox's Today, Explained newsletter characterises CTE as a significant occupational hazard akin to black lung disease in coal miners.
- [19]
According to the Aspen Institute's State of Play report, tackle football participation among Americans ages 13 to 17 decreased 9% from 2019 to 2024 and has fallen behind tennis in that cohort.
- [20]
Flag football participation among children ages 6 to 12 grew 13.6% from 2019 to 2024 while tackle football play dropped 7% in the same age group.
- [21]
Last year 83 of the top 100 rated US television shows were NFL games, up from 72 in 2024.
- [22]
The 235 examined brains represent about 26.8% of the 878 former players who died in 2016-2021.
- [23]
643 of the 2016-2021 decedents had no brain examination.
- [24]
The authors suggest the real CTE rate among former NFL players may be closer to 90%.
Sources
2 independent publishers whose own reporting we read for this story.
- forbes.comNew Study: 1 In 4 NFL Players Had CTE At Death
1 article · August 25, 2026
- vox.comFootball is dangerous. Parents are finally steering their kids away from it.
2 articles · August 25, 2026
Topics and entities
Topics
- Occupational Safety Regulation
- Sports Injury Liability
- Neurodegeneration Diagnostics
- CTE Epidemiology
- Youth Sports Participation
- Study Design and Selection Bias
Entities
- Occupational Safety and Health Administration
- Concussion & CTE Foundation
- Binney and Bachynski 2019 Model
- Chuck Klosterman
- UNITE Brain Bank
- US Centers for Disease Control
- Boston University
- National Football League
- Mass General Brigham
- Chronic Traumatic Encephalopathy