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A study in JAMA Network Open used statistical modeling to estimate that 74.5% of former NFL players who died from 2008 through 2023 had CTE. The estimate adjusts for selective brain donation, but applies only to that deceased group and depends on assumptions; it does not establish prevalence among living players or athletes at other levels.
A statistical model estimates that 74.5% of former NFL players who died from 2008 through 2023 had chronic traumatic encephalopathy (CTE), according to a study published in JAMA Network Open. The researchers adjusted results from donated brains for possible selection bias, but the estimate applies to deceased former players in that period—not to living NFL players or athletes generally.
Yorghos Tripodis, PhD, of the Boston University School of Public Health, and colleagues combined data from the UNITE brain bank with national death records. They identified 2,362 deceased former NFL players: 396 had donated their brains and 1,966 had not. Of 387 donors with an assessed brain sample, 362, or 93.5%, had CTE at autopsy. The gap between that donor figure and the modeled estimate reflects the researchers’ effort to account for who is more likely to donate.
The model estimated CTE prevalence at death at 74.5%, with a 95% confidence interval of 69.6% to 78.3%. It also estimated all-cause dementia at 27.2% (95% confidence interval 22.6% to 31.6%). The analysis calculated a median selection ratio of 4.97: former players with cognitive symptoms were estimated to be about five times more likely to have their brains donated than those without symptoms.
The study’s authors said the findings suggest that selection bias inflates donor-based estimates, but is unlikely to account for all the CTE pathology found in this group. CTE can currently be identified only through examination of brain tissue after death. The study does not estimate the stage of CTE in each person or establish how common it is among people who are still alive.
What the Estimate Can Tell Families
The study addresses a central problem in CTE research: donated brains are not a random sample. Families may be more likely to donate when a player experienced cognitive or behavioral symptoms, which can make the share of diagnosed cases among donors a poor guide to prevalence across all former players. By modeling that selection process, the researchers offer a broader estimate for a defined group than the raw donor percentage alone.
Still, 74.5% is an estimate, not a count of confirmed diagnoses across every former NFL player who died in those years. It relies on assumptions about why families donated and how symptoms were recorded. The result adds evidence about CTE pathology among deceased former NFL players, but it cannot say which living players have CTE or predict an individual’s health or future symptoms.
The distinction matters for families and former players weighing what the findings mean for care. Rachel Grashow, PhD, MS, of Harvard, said the research draws attention to roughly 20,000 living former NFL players, some of whom have cognitive symptoms or dementia diagnoses. She emphasized that health issues associated with head injury may be treatable, making clinical evaluation relevant even though CTE itself cannot be confirmed in a living person.
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How Brain Donation Shapes the Evidence
The study analyzed people who had died, rather than tracking CTE diagnoses in a representative group of living players. The researchers reported a mean playing career of 5.1 years; 41.1% of the deceased players were at least 80 years old at death. These characteristics describe the group used in the analysis and should not be assumed to represent every former NFL player.
Because CTE is diagnosed by autopsy, research has relied heavily on families who choose to donate a player’s brain. The model assumed donation was primarily influenced by cognitive symptoms, using dementia recorded on death certificates and an adjustment for mild cognitive impairment. Under its calculation, symptomatic former players were about five times as likely to have a donated brain as those without such symptoms. That ratio is a model result, not a direct measure of every family’s decision-making.
Outside experts interviewed by MedPage Today said the study’s scope is limited. Marc Weisskopf, PhD, ScD, of Harvard, noted that the deaths included in the analysis represented about 10% of those that could have occurred in the period and cautioned that the assumptions affect the estimate. Julie Stamm, PhD, of the University of Wisconsin-Madison, said the findings do not estimate CTE prevalence among athletes in other sports or at lower levels of play.
“Selection bias materially inflates donor-based prevalence estimates but is unlikely to fully explain the high burden of CTE neuropathology among this population.”
— Yorghos Tripodis and co-authors
Limits of the CTE Estimate
The estimate depends on assumptions about what leads families to donate a brain and whether cognitive symptoms were adequately captured in the records used for adjustment. The study cannot show how closely those assumptions match every case. Weisskopf also cautioned that the deaths analyzed were about 10% of all that could have occurred during the period, and suggested CTE might be less common among players who are still alive and will die later.
The analysis does not determine CTE prevalence among living former players, identify an individual’s CTE status, or estimate the disease’s stage. It also says nothing about prevalence in college, high school, youth, or professional athletes in other sports. Although greater lifetime exposure to repetitive head impacts has been linked to higher CTE risk, the source material provides no prevalence estimate for those other groups.
CTE is a postmortem neuropathological diagnosis. The model’s estimate should not be read as showing that three in four current or living former NFL players have a confirmed condition, nor does it establish that every player with a history of head impacts will develop CTE.
Follow-Up for Living Former Players
The study’s next practical implication is attention to the health of living former players, rather than treating a postmortem estimate as a diagnosis. Grashow said the Harvard Football Players Health Study cohort includes more than 5,000 former players and pointed to conditions such as sleep apnea, high blood pressure, low testosterone, depression, anxiety, and tinnitus as health concerns that can be evaluated and treated. She said managing such conditions may help address risks related to cognitive health and dementia.
Researchers can continue testing how well donation-bias models estimate prevalence as additional data become available. For readers, the key limits remain: the 74.5% figure concerns deaths from 2008 to 2023, rests on statistical assumptions, and does not provide a living-player diagnosis or a reliable estimate for other athlete populations. The study material does not identify a specific next publication date or planned follow-up result.
Key Questions
Does the study show that 74.5% of living former NFL players have CTE?
No. The estimate concerns former NFL players who died from 2008 through 2023. CTE is diagnosed through examination of brain tissue after death, and the study did not measure prevalence among living players.
Why is the estimate lower than the percentage of brain donors with CTE?
Of 387 donors with an assessment, 362 (93.5%) had CTE. The researchers modeled the possibility that families of players with cognitive symptoms were more likely to donate, then adjusted the estimate for that selection bias. The resulting prevalence estimate was 74.5%.
Does the study say how severe the CTE was?
No. It estimated whether CTE was present, not the stage of CTE in each person. The study therefore does not establish how severe the disease was or what effects it had on an individual’s daily life.
Can the findings be applied to college or youth football players?
No prevalence estimate for those groups was provided. The analysis focused on former NFL players who died during the study period; the results do not establish CTE prevalence among athletes at lower levels or in other sports.
What can living former players do with this information?
The study is not a diagnostic test for an individual. A former player with health or cognitive concerns can discuss evaluation with a qualified health professional. Grashow highlighted potentially treatable conditions, including sleep apnea, high blood pressure, depression, and anxiety, as areas that may warrant attention.
Source: medpagetoday.com
