Sports and Statistics: Correlating Football to Brain Injury

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Wharton's Dylan Small, Raiden Hasegawa and Sameer Deshpande discuss their research on high school football players and the risk of developing CTE.

Much attention has been given in recent years to professional athletes who develop chronic traumatic encephalopathy, a degenerative brain disease known as CTE, after years of taking repeated blows to the head during their sport. The cases are most common among boxers and football players, and the NFL has taken some steps to deal with the occurrence of the disease. But what about the brain health of football players whose athletic careers end after high school or college? In, “Association of Playing High School Football With Cognition and Mental Health Later in Life,” which was published in the journal JAMA Neurology, Wharton statistics professor Dylan Small and doctoral students Raiden Hasegawa and Sameer Deshpande used statistical analysis to research the long-term effect of playing football. They spoke to the Knowledge@Wharton radio show, which airs on SiriusXM channel 111, about what they found in their study.

An edited transcript of the conversation follows.

Knowledge@Wharton: What was the starting point for this research?

Raiden Hasegawa: We use the Wisconsin Longitudinal Study, which followed high school students in Wisconsin from the 1950s. This was an interesting data set for us because people are interested in later-life cognition when it comes to playing football, so we’ve got to go back far enough in time to find high school football players. We compared high school football players to non-high school football players and looked at various cognitive outcomes down the line.

Knowledge@Wharton: Were these specifically individuals who played high school football and did not go on to play college? Or was there a mix in there?

Hasegawa: There was a mix. All we knew was whether or not they played high school football. We used yearbook data to determine whether or not they played high school football. One of the novel designs of the experiment was that we thought possibly just playing a sport has an effect on your cognition in the long run.

We compared these high school football players to people who played a non-contact sport such as baseball. We also compared them to high school students who didn’t play any sport at all. The hope was that we could capture some unobserved differences between people who played sports and people who didn’t. If we saw a similar effect, then that would build evidence for or against there being some sort of effect.

Knowledge@Wharton: The outcome was that there wasn’t a whole lot of data showing a significant increase in cognitive impairment or mental health issues by a lot of these people, correct?

Sameer Deshpande: Right, exactly. Raiden mentioned that we compared the outcomes of football players to the people who didn’t play football, but also rolled into that comparison was that we were really careful to control for a lot of confounding. Maybe there were some differences back before they started playing football or right before they graduated from high school that could have predisposed them or might have some impact later on. So, there might be another causal mechanism not necessarily through football. We were pretty careful to try to control for a lot of these confounders. I think the big one was adolescent IQ, how they ranked in high school, how many years of education they wanted to go into afterwards, whether they served in the military or planned to serve in the military. We had a whole list.

Dylan Small: The value of using this data from Wisconsin was that they had done a very thorough survey of the students’ activities and what they were like as a high-schooler so that we could match football players who were similar to non-football players when they were in high school.

Knowledge@Wharton: Can you take this Wisconsin data and extrapolate as to what could be the potential in other parts of the country?

Deshpande: I think you can, but you need to take it with a grain of salt, right? Football changed dramatically in the mid-1960s.

Small: There could be differences in the Wisconsin population versus other places, but it’s probably reasonable that football wasn’t that different in different high schools.

Deshpande: Right, exactly. If you can find a population that played football similar to the way they played it in Wisconsin in the mid-1950s, and maybe the geographic differences aren’t too big or the population of Wisconsin students is similar to this other state, then I would feel safe making that extrapolation.

But if you said, what about people who played in California in the 1970s, I would pump the brakes a little bit because the game changed. It’s a different population. Now, people are bigger, stronger, faster. The game is totally different. So, I wouldn’t necessarily extrapolate it all of the way.

Knowledge@Wharton: How do you take this data and bring it forward, which is probably the biggest question people have surrounding the sport today. The athletes are bigger and stronger and faster and hit harder. There are several cases where CTE has cost an athlete his life.

Deshpande: I think not necessarily the data but the method and design is what can be carried forward. What made this study pretty special was we had all of this information about what did people do before or concurrent with the time they started playing high school football, so we were able to follow them throughout their life.

If you take the same study design and found there was a longitudinal study of people maybe in the 1970s or 1980s or 1990s, you can try to do the same type of analysis and carry that forward. You will get some information about how the safety or the risks of football have changed over time.

Small: Which is what we’re currently trying to do. We’re now looking into a cohort of people who played in the 1990s.

Knowledge@Wharton: What has been the reaction to your study and the fact that, at least back in the 1950s with this subset, there wasn’t a significant issue with cognitive impairment?

Hasegawa: One thing that might be directly relevant is that people who played football in the mid-1950s are now maybe in their late 70s. This has some useful information for them if they were worried about their mental health or cognitive health related to the football they played.

Small: One of the concerns that has been raised by mental health professionals is that some people who played football maybe are experiencing depression for something that is difficult in their life. They are thinking that they have CTE and it’s a sort of irreversible thing, whereas it might be just be a depression, which is very treatable.

Knowledge@Wharton: There were so many other factors that could be involved, not even including what happened on the football field to this individual. There’s data that can be brought forward. It’s not perfect, but at least it’s a start.

“There are people who looked at this study and said football is totally safe, this is a vindication. I don’t think that’s a reasonable conclusion.” –Sameer Deshpande

Deshpande: There are people who looked at this study and said football is totally safe, this is a vindication of everything we knew about football. I’m certainly not saying that, and I don’t think that’s a reasonable conclusion from this study. But there are people who do recognize that this is a first step. We have a whole lot of research to do, and this is maybe the heartbreaking part, is that people are concerned there might be risks, but the research is just getting started.

Hasegawa: Yeah, the challenge of this type of question is you can’t really do a randomized control trial. You can’t say you are going to play football, you are not going to play football, and flip a coin. The hope with this study was that we did a good job of comparing people who are similar in other regards like  IQ, educational plans. And the hope was that even though we didn’t have a randomized control trial, we’re just observing these people who made decisions to play football for reasons that would affect their cognition later in life, that we could maybe key in on at least better estimate an average difference between players.

Knowledge@Wharton: Dylan, you mentioned that you are trying to do this now with athletes that played in the 1990s. How much available data is there from that group compared with the Wisconsin study?

“This study, even though it’s limited, is important in the sense that it’s the only data that we really can look at that shows long-term effects.” –Dylan Small

Small: The study we’re looking into, the data is pretty rich in terms of collecting a lot of information about a lot of people. The one caution is now they are people in their late 30s, so there may not have been time for the effects of football to play out. I think that’s a big challenge right now is that the game is changing, but at the same time it takes a long time to see the long-term effects. That’s why we think this study, even though it’s limited, is important in the sense that it’s the only data that we really can look at that shows its long-term effects.

Desphande: I would make the point here that the Wisconsin data wasn’t originally collected to study football players. The study ran out of the University of Wisconsin Madison, I think, and they were really interested in socioeconomic factors. Dylan had worked with this data set before and noticed they recorded whether they played football, and they did a whole battery of cognitive and mental health assessments later in life, so maybe we can use this data set.

In the same way, we were going to start looking at a data set that was collected of adolescents in high school and middle school in the mid-1990s, and that was really to study how the health of adolescents change as they grow into adulthood. We also have indicators of whether they played football, and we know some of these other health indicators that have been measured, so we said we can leverage this information. To our knowledge, there hasn’t been a longitudinal study that is dedicated to football, but there are other longitudinal studies that we can leverage.

Knowledge@Wharton: It would seem you have the potential of being able to get good data now because of how we are such a data-driven society. It makes it easier to take that formula and bring it forward to 2011, 2015, whatever year you see as the potential starting point. Obviously, it does have to be a bit of a retrospective look because you don’t see a lot of these issues playing out until you are 35, 40, 50 years of age.

Small: Right, and I think one of the big limitations we had, and hopefully future data collection can address, is we just had a measure of whether they played football. We didn’t have a measure of the position they played or the history. I think that’s one of the big questions. Are there particular positions, particular concussion histories that might carry particularly high risks?

Knowledge@Wharton: You guys studied football, but there are similar concerns with a lot of other sports out there. The U.S. Soccer Federation changed the rules so kids are not able to head the ball until they are at least 12 years old. High school wrestling is another one where there are more concerns about injury now than before.

Hasegawa: That’s right. One of the points we wanted to make with this paper was that, whether or not this study can be extrapolated to football players today, you can say something about people who play high school sports or any sports that had a similar level of risk for head injury as those who played high school football in the 1950s, which is probably a much broader category of adolescent athletes.

Knowledge@Wharton: There is research that shows there are benefits from playing sports in terms of camaraderie, leadership, teamwork. It’s just weighing the balance between those benefits and the potential health issues that are out there.

Hasegawa: Yeah, absolutely. I think in the cohort that we studied, we found that the people who played high school sports also reported being somewhat more physically active in their mid-30s. And that might have some protective health effect.

Small: There’s a lot of research showing that physical activity is very good for later-life health.

Knowledge@Wharton: Looking at the data, you needed to look back at the 1950s, maybe the 1960s, because those people have lived most of their lives and you can correlate what issues that they had.

Deshpande: Absolutely. When we started the study, we asked, “How much can we extrapolate this?” We thought if we find something that there is a significant harm, then you might rightly argue football now is maybe more dangerous than it was before, and then this is a cause for a concern. We didn’t find anything. We didn’t find a significant harm. We didn’t find that football players were more depressed or more impaired than their non-football playing counterparts. That’s still useful information to the cohort, and if you can roll this back to younger and younger cohorts, we can start to get a sense of either the life history of any potential effects of playing football. People in the 1960s were concerned about skull fractures and breaking their necks, so they said wear these hard-shell helmets. That led to people saying, now I can run into people with my head. There’s a lot of knock-on effects.

Hasegawa: I’m not an expert on football technique, but I’m sure coaching in terms of how to hit and how to tackle has changed over the past several decades. I’m sure that has had an effect on the type of head injuries that people are seeing in football at all levels.

“With football, I don’t know if I would say it’s as dangerous as smoking.” –Raiden Hasegawa

Deshpande: Football is an evolving sport, right? In the last five years, we’ve gotten so much more information about the potential risks of head injuries and whatnot. You see people at all levels asking whether children should be playing tackle football, and this is sort of what motivates the study. We’ve got to start somewhere, so let’s start with the data we have. We acknowledge the limitations, and we take that and move on to the next study and start to build up this space of research and knowledge to try to get a better understanding of what is really going on.

Small: That’s our intention. To follow up on Raiden’s point, it’s almost speculative but if, for example, soccer today involves less head trauma than football in the 1950s, then our study might be saying something about soccer today.

Knowledge@Wharton: The number of kids playing youth football has dwindled in the last few years. More kids are playing soccer and a variety of other sports. This research has the potential to change the course of what we think about football in the next 30 to 40 years.

Hasegawa: Absolutely. You will hear people who defend football, and I’m not saying you shouldn’t. I think it’s a good sport. I never played. But people will say that it has a lot of benefits: camaraderie, teamwork, leadership, fitness. But it also has the risks. We’re trying to get a better understanding of these risks. A parent whose kid wants to play football has to balance these risks in a way that only they can.

It’s unfortunate that we have to fall somewhere in the middle. Football is risky, and we’re not saying that it isn’t. But on the spectrum of risks, if I had to hazard a guess, I would say your risk for long-term effects are maybe not as obvious and clear as, say, smoking. You pick up a pack of cigarettes, you start smoking, you continue smoking, you will probably develop something down the line. With football, I don’t know if I would say it’s as dangerous as smoking.

Small: What we also want to get at is what is the dose of exposure? Maybe playing a certain amount of recreational football is not putting you at much risk, but playing professional football is putting you at a lot of risk. That’s the future research that we hope to really figure out.

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accessed August 23, 2017. http://knowledge.wharton.upenn.edu/article/high-school-sports-cte/


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