A Decision-Analytic Approach to Addressing the Evidence About Football and Chronic Traumatic Encephalopathy

Abstract

Doubts can be raised about almost any assertion that a particular exposure can lead to an increase in a given adverse health effect. Even some of the most well-accepted causal associations in public health, such as that linking cigarette smoking to increased lung cancer risk, have intriguing research questions remaining to be answered. The inquiry whether an exposure causes a disease is never wholly a yes/no question but ought to follow from an appraisal of the weight of evidence supporting the positive conclusion in light of any coherent theories casting doubt on this evidence and the data supporting these. More importantly, such an appraisal cannot be made sensibly without considering the relative consequences to public health and economic welfare of specific actions based on unwarranted credulity (false positives) versus unwarranted skepticism (false negatives). Here we appraise the weight of evidence for the premise that repeated head impacts (RHIs) in professional football can increase the incidence of chronic traumatic encephalopathy (CTE) and, in turn, cause a variety of cognitive and behavioral symptoms. We first dismiss four logical fallacies that should not affect the appraisal of the weight of evidence. We then examine four alternative hypotheses in which RHI is not associated with CTE or symptoms (or both), and we conclude that the chances are small that the RHI→ CTE→ symptoms link is coincidental or artifactual. In particular, we observe that there are many specific interventions for which, even under a skeptical appraisal of the weight of evidence, the costs of a false positive are smaller than the false negative costs of refusing to intervene.

Applying the Bradford Hill Criteria for Causation to Repetitive Head Impacts and Chronic Traumatic Encephalopathy

“…If we do something, and we learn later that the hazard was not really a hazard, there may be harm done. If we do nothing, and the hazard was in fact a hazard, there will be harm done of a very different sort (163).…”

Toward Complete, Candid, and Unbiased International Consensus Statements on Concussion in Sport

“…Similarly, the statement that "A cause-and-effect relationship has not yet been established between CTE and sports-related concussions or exposure to contact sports" is incomplete: a more honest summary might have read "The strong statistical associations found between CTE and SRCs or exposure to contact sports may not represent a true cause-and-effect relationship, but at present attempts to attribute these associations to confounding, bias, or artifacts have not been persuasive". 20 We also note that prospective longitudinal studies of a well-characterized cohort, the claimed sine qua non of the establishment of a causal link between repetitive head trauma and later-in-life neurodegenerative diseases, are not only impractical but also unethical in light of the significant probability of patient harm. As many as seven decades might separate a particular individual's exposure and the emergence of neurological signs and symptoms.…”

Examining later-in-life health risks associated with sport-related concussion and repetitive head impacts: a systematic review of case-control and cohort studies

“…In recent years, there have been many published narrative and systematic reviews relating to possible long-term effects of SRC and participation in contact, collision and combat sports. 1-13 29 31 34 37-41 47 49 50 53 55 100 101 The topics of those reviews included neurological diseases, CTE, psychiatric disorders, suicide, neuroimaging and neuropsychological outcomes. The authors of past reviews have often concluded that the general quality of the evidence was low, and that high-quality cohort studies were needed.…”