A recent study conducted by Boston University researchers and published in the Journal of the American Medical Association has caught the public’s attention. And, as a result, concern about American football’s impact on the brain — namely when it comes to chronic traumatic encephalopathy, or CTE — has heightened once again.

CTE is the medical term used to describe the pathologic changes found during autopsy in the brains of athletes who have been exposed to repeated head injuries and concussions. Prior to death, many of the individuals later found to have CTE had concerning symptoms of chronic neurological impairment with symptoms that often included headaches, trouble concentrating, confusion and difficulty controlling emotions. In many ways, these symptoms are difficult to definitively assign to CTE because individuals behaved very similarly to those with other diseases and conditions that affect the brain. Depression, substance abuse, other forms of dementia and post-traumatic stress disorder are examples of diagnoses that may result in similar symptoms — with or without a history of exposure to repetitive head injury. Currently, the only reliable way to confirm a suspected CTE diagnosis is after death, via autopsy.

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The BU researchers set out to determine what the neuropathological and clinical features were on a case series of deceased athletes whose brains had been donated for the purpose of research. The researchers’ findings indicated that CTE was present in 177 players across all play levels, which included 110/111 former NFL players.

Without the ability to test for CTE in the living, it’s difficult for the medical community to conclusively connect the abnormalities found on the pathology of a brain in a deceased person to the clinical symptoms that present in a live human. This forces neuroscientists to ask quite a few questions: Are problems with cognition, depression and violent tempers in football players all caused by CTE? Or could there be other factors, like a genetic predisposition to certain diseases or conditions, contributions from the use of performance enhancing drugs, other inherent traits or consequences from participation in contact and collision sports also at work? Although none of the answers is definitive, I strongly believe that the development of CTE in the brains of football players is likely multifactorial.

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Now, that assertion is not to minimize the work or findings of this study’s authors. Far from it, actually. I applaud the research, and it’s precisely what we need in order to come to more concrete conclusions down the road. But we aren’t quite there yet. It’s important to note that the Boston University study was conducted on the donated brains of 202 American football players. These brains were donated for a reason. In this case, it was people who were already concerned about the effects of head injuries on their brains. Scientifically speaking, this is considered a “convenience sample,” which can result in selection bias, meaning that the subjects studied are from a population conveniently able to participate in the study. Of course, the study authors recognize this fact and cite it in the conclusion summary of the study: “In a convenience sample of deceased football players who donated their brains for research, a high proportion had neuropathological evidence of CTE, suggesting that … CTE may be related to prior participation in football.” This is critically important. When the public reads media headlines that state: “CTE found in 99 percent of studied brains from deceased NFL players,” it understandably leads people to think: “If you play in the NFL, you’ll get CTE.” Or worse: “If my child plays tackle football, he will get CTE.” But that isn’t necessarily the case. Remember, this study had a selection bias from the start.

When it comes to public consumption of medical research, it’s important to understand the difference between correlational and causational research studies. As this study’s authors point out: “CTE may be related to prior participation in footbal;” this is a correlational study. It isn’t definitive. It’s not saying CTE is caused by prior participation in football. A definitive statement like that is typically subject to much stronger, longer and more rigorous scientific investigation, and I caution people against taking a causational interpretation of a correlational study.

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Of course, the public may still wonder: What do I do with this information? How do I use it to make decisions for my own family, or for loved ones who play or are interested in playing football? Well, we’re getting there. We’re beyond the early phase of education, when concussion and CTE were certainly happening but weren’t discussed or addressed. Education is key, and the medical community, the NFL and football at every other level understands the seriousness of brain injury. We’ve got a long way to go, but studies like these are important steps toward future clarity.

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The Impact of Football on the Brain originally appeared on usnews.com