Setting aside Mr. Ryan’s dubious analysis, though, there is a legitimate enough reason to wonder if getting bonked in the head over and over causes long-term damage. Let’s leave behind the anecdotes. What does the science say?

Unfortunately, not much. A recent article by Stella Karantzoulis and Christopher Randolph in Neuropsychology Review examined the evidence. CTE isn’t a “new” disease; it’s been recognized for several decades in boxers and referred to as “dementia pugilistica.” However, the trouble with drawing any connection between sports concussions and neurodegenerative disease is the fact that most studies have been done, as the authors say, out of convenience. In other words, typically only athletes who were suspected of having CTE are autopsied. This introduces an enormous bias into the rather limited evidence base.

Other problems for a football-CTE link include: (1) The rate of suicide among former NFL players is actually lower than the population at large; (2) the symptoms of CTE are similar to other neurodegenerative diseases, such as Alzheimer’s; and (3) there is no medical consensus about the distinguishing features of CTE. For instance, the presence of a clump of proteins called tau in the brain (tauopathy) is used to diagnose CTE, but tauopathy also exists in Alzheimer’s and nearly two dozen other diseases.