Digital illustration of a football helmet revealing brain damage, symbolizing the risk of CTE in football.

CTE in NFL Players: Unpacking the Prevalence and Risks

Nico Varela in Health & Wellness June 2025 • 3 min read.

"A closer look at new data on chronic traumatic encephalopathy among former football players and what it means for the future of the sport."

In July 2017, a study published in JAMA revealed that 110 out of 111 deceased NFL players (99%) showed neuropathological evidence of chronic traumatic encephalopathy (CTE). This progressive neurodegenerative disease, linked to repeated head trauma, sparked widespread concern and media attention.

However, diagnosing CTE is currently only possible post-mortem, raising questions about the representativeness of these findings. Players exhibiting CTE symptoms may be more inclined to donate their brains for research, potentially skewing prevalence estimates. The original study acknowledged this selection bias but didn't quantify its impact.

This article explores new research published in Neurology, which re-examines the JAMA study's data to provide a more nuanced understanding of CTE prevalence in former NFL players. By accounting for potential selection bias, this analysis offers a broader perspective on the risks associated with professional football.

Estimating CTE: Methods and Challenges

Digital illustration of a football helmet revealing brain damage, symbolizing the risk of CTE in football.

The recent analysis utilizes data from a cohort of 1,142 deceased NFL players who were eligible to participate in the original CTE study. The researchers focused on addressing the selection effect, acknowledging that not all players are equally likely to donate their brains. They highlight the importance of considering this bias when interpreting CTE prevalence.

Correcting for this selection effect requires estimating the probability of brain donation among players with and without CTE. The analysis uses two key parameters:

The probability that a player with CTE donates their brain.
The ratio of donation probabilities between players with and without CTE.

By varying these parameters, the researchers generated a range of plausible CTE prevalence estimates. The findings emphasize that the commonly cited 99% figure might be an overestimation due to selection bias.

Interpreting the Results: What Does This Mean for Football?

The analysis provides a more realistic range of CTE prevalence among deceased NFL players. While the exact number remains uncertain, the study underscores the importance of accounting for selection bias in research. These findings can inform discussions about player safety, rule changes, and long-term health management in professional football. Future research, including the development of in vivo CTE biomarkers, will further refine our understanding of this complex issue.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

Everything You Need To Know

What is CTE, and why is it a concern for NFL players?

CTE, or chronic traumatic encephalopathy, is a progressive neurodegenerative disease linked to repeated head trauma. In the context of NFL players, this is particularly concerning due to the high-impact nature of the sport, which exposes players to frequent head injuries. CTE can lead to various neurological and psychological symptoms, affecting the long-term health and well-being of former players. Diagnosing CTE is only possible post-mortem, which complicates the understanding of its prevalence and impact.

How was the initial prevalence of CTE determined among NFL players, and what were the key findings?

A study published in JAMA in July 2017 revealed that 110 out of 111 deceased NFL players (99%) showed neuropathological evidence of CTE. This finding, highlighting a very high prevalence, sparked significant concern and media attention. However, the study acknowledged potential selection bias, recognizing that players with CTE symptoms might be more likely to donate their brains for research, which could skew the prevalence estimates.

What is selection bias in the context of CTE research, and how does it affect the interpretation of findings?

Selection bias refers to the systematic error introduced when the sample studied is not representative of the entire population. In CTE research, it arises because players exhibiting symptoms of CTE may be more inclined to donate their brains for research. This means that the sample of brains examined might have a higher proportion of individuals with CTE than the overall population of deceased NFL players. Consequently, the initial 99% figure might be an overestimation due to this bias, making it critical to account for it in the research.

What methods are used to estimate CTE prevalence while accounting for selection bias?

The recent analysis in Neurology re-examines the JAMA study's data to provide a more nuanced understanding of CTE prevalence in former NFL players. The research utilizes data from a cohort of 1,142 deceased NFL players who were eligible to participate in the original CTE study. The analysis employs two key parameters to correct for selection bias: * The probability that a player with CTE donates their brain. * The ratio of donation probabilities between players with and without CTE. By varying these parameters, researchers generate a range of plausible CTE prevalence estimates, providing a more realistic view of the risks.

What are the implications of this research for the future of football and player safety?

The findings provide a more realistic range of CTE prevalence among deceased NFL players, emphasizing the importance of accounting for selection bias in research. This understanding can inform discussions about player safety, rule changes, and long-term health management within professional football. The study highlights the need for a nuanced approach to the issue, acknowledging that the exact prevalence remains uncertain. Future research, including the development of in vivo CTE biomarkers, will further refine our understanding of this complex issue, paving the way for improved player safety measures and healthcare strategies.