110/111 is a curious kind of number — both potentially misleading and yet highly informative. Using these case reports to estimate how widespread CTE and its hallmark symptoms of mental decline and mood disturbances will be over the next several decades is tricky because the sample isnot representative; the 111 whose families sought autopsies for their next-of-kin tend to include those players who suspected they might have CTE because of symptoms they suffered during retirement.
Unfortunately, advocates on both sides are desperately misusing the 110/111 statistic. A few claim we will eventually learn that a “shockingly high percentage” of all NFL players will develop CTE, but this may over-rely on the skewed nature of the first 111 autopsies.
Critics lacking public health training are routinely making four illogical claims to “manufacture doubt” about this emerging issue.
First, I was buffeted with repeated claims that “some players never developed CTE despite long careers.” I hope it’s obvious that this is a completely useless fact. A risk factor never has to result in disease or injury among everyone for it to cause grave harm in a few or in many victims; that’s the very definition of “risk” (as opposed to certainty).
Imagine the claim that “smoking can’t cause lung cancer because I heard of someone who smoked for 60 years and died in a car crash” and the derision that would, or at least should, dismiss that fallacy. Similarly, our draft OSHA study was criticized because we didn’t mention the mirror-image observation — that it may be possible to develop CTE without ever having experienced repeated head trauma. Again, change this utterance to “smoking can’t cause lung cancer because radon can,” and one should shudder at the illogic.
Besides, it’s not even clear that a single human being has ever developed CTE without some history of head trauma: the Mayo Clinic examined 264 specimens from a brain bank, and found CTE in 21 of the 66 persons who had been contact-sport athletes, but not in even a single one of 198 matched control subjects without contact-sport experiences.
Other skeptics, using two similar spasms of illogic, actually argue that although CTE is associated with devastating symptoms, the brain lesions themselves may be “tiny abnormalities [that] might not have any specific clinical significance.” Again, anecdotes about a specific person with CTE lesions and no symptoms, or the opposite fact that many people can have similar symptoms without CTE lesions, are just noise, not signals of anything relevant.
And it turns out, we can learn much about the true risk of CTE among football players by starting with, though not accepting at face value, the series of 110 case reports. We can readily estimate thelowest possible risk, simply by exploring the unrealistic best-case scenario that not a single additional CTE case will ever be found among the rest of the players who were in the League at the same time as the 110 were.
Using individual player data from the NFL on the number of his team’s snaps each player was on the field for, and on the length of his career in the League, I estimated that there was a total of about 12,000 player-careers worth of on-field activity (about 26,000 different players suited up during this time period, but many of them played only occasionally and in a very few games). So 110 cases out of 12,000 players yields a best-case risk of 0.0092, or just under a 1 percent risk.
A 1-in-100 chance (at the bare minimum) of a grave disease caused by environment or occupation is a huge risk that any law or regulation would deem unacceptable. The Supreme Court instructed OSHA in 1980 that occupational disease risks above one chance per thousand must be worthy of regulation, and Congress has instructed the EPA in various laws to regulate cancer and other risks exceeding one chance per million.
What, then, could OSHA do to reduce this significant risk of disease, in football and in other occupations (logging, commercial driving, the military) where repeated head trauma is commonplace? OSHA could propose regulatory limits for the cumulative head-trauma forces workers could undergo, just as it has regulated various chemicals based on case series of as few as seven workers afflicted with cancer or sterility, and having a common exposure.