CTE Found in an Estimated 74.5% of Deceased NFL Players After Adjusting for Brain Donation Bias
A new study published in JAMA Network Open estimates that nearly three-quarters of former National Football League (NFL) players who died between 2008 and 2023 had chronic traumatic encephalopathy (CTE) neuropathology. Importantly, the researchers accounted for a major limitation in previous studies: the tendency for individuals with cognitive or behavioural symptoms to be more likely to donate their brains for postmortem examination.
The study, titled “Bias-Adjusted Prevalence of Chronic Traumatic Encephalopathy Among Deceased National Football League Players,” provides a population-level estimate that is lower than the very high rates reported in selected brain-donation cohorts, but still indicates a substantial burden of CTE among deceased former professional football players.
Why previous estimates may have been inflated
CTE is a progressive neurodegenerative disease associated with repetitive head impacts (RHIs), which can occur during contact sports, military combat and other forms of repeated head trauma. At present, CTE can only be definitively diagnosed through examination of brain tissue after death.
Much of the existing evidence on CTE in professional football players comes from donated brains, particularly those included in the Understanding Neurologic Injury and Traumatic Encephalopathy (UNITE) Brain Bank. However, people who experience cognitive, mood or behavioural symptoms may be more likely to participate in brain donation. This creates selection bias, also known as registry bias, and can lead to an overestimation of disease prevalence.
For example, an earlier study reported CTE in 110 of 111 former NFL players whose brains were examined. Such findings describe the selected donor group, not necessarily the entire population of former players.
How the researchers estimated prevalence
Led by Julia Gallini and colleagues, the cross-sectional study combined data from the UNITE Brain Bank with National Death Index records. The analysis included 2,362 former NFL players who died between January 2008 and December 2023.
Of these, 396 were brain donors and 1,966 were non-donors. Among the 387 donors with determined CTE status, 362 (93.5%) had CTE neuropathology.
To account for the likelihood that players with cognitive symptoms were more likely to donate their brains, the researchers estimated a selection ratio using dementia-related causes of death and population-level estimates of mild cognitive impairment (MCI) and dementia. They used Poisson regression, adjusting for factors including age at death, race, playing position, years played, Pro Bowl appearances and Hall of Fame status.
Key findings: CTE prevalence remains high after adjustment
After adjusting for differential brain donation, the estimated prevalence of CTE neuropathology was 74.5%, compared with 93.5% in the examined donor group.
The researchers also conducted nine sensitivity analyses to test the robustness of their estimates. Depending on the assumptions used, adjusted CTE prevalence ranged from 70.3% to 86.1% in the principal sensitivity analyses. A particularly conservative lower-bound analysis estimated prevalence at 63.7% (95% CI: 57.2%–68.9%).
The estimated prevalence of all-cause dementia history during life was 27.2%. This is distinct from CTE itself: the study could not establish how much of the dementia burden was specifically caused by CTE.
What do these findings mean?
The findings suggest that selection bias contributes substantially to the exceptionally high CTE rates reported in earlier brain-donation studies. However, correcting for this bias does not eliminate the evidence of a considerable burden of CTE neuropathology among deceased former NFL players.
The study also highlights the importance of distinguishing between the presence of CTE pathology in the brain and its clinical consequences. Not everyone with CTE neuropathology necessarily develops dementia or experiences recognisable symptoms. The estimated 74.5% includes all stages of CTE and should not be interpreted as the proportion of living NFL players experiencing symptomatic disease.
Important limitations
The estimates rely on assumptions because direct clinical and neuropathological information was unavailable for non-donors. Dementia-related causes of death and population-level MCI estimates were used as proxies for cognitive symptoms. Other unmeasured factors could also influence brain donation.
Furthermore, the results apply specifically to deceased former NFL players who died during the 2008–2023 study period. They cannot be directly extrapolated to currently living players, college or high-school football players, or people participating in other contact sports.
The study also does not establish whether CTE independently increases mortality risk.
The bigger picture
This research provides an important methodological advance in understanding CTE prevalence by addressing selection bias in brain-donation studies. Its central finding is that although earlier estimates may have been inflated, the burden of CTE neuropathology among deceased former NFL players remains substantial.
The authors emphasise the need for further research into the mechanisms, clinical manifestations and prevention of CTE, including studies of football players at lower levels of participation.
Source: Gallini J, et al. Bias-Adjusted Prevalence of Chronic Traumatic Encephalopathy Among Deceased National Football League Players. JAMA Network Open. Published October 28, 2026;9(10):e2640884.
Read the original research paper
Editorial note: The study estimates postmortem neuropathological prevalence, not the prevalence of clinically diagnosed or symptomatic CTE among living football players.
