Utility of providing a concussion definition in the assessment of concussion history in former NFL players.

The study was cross-sectional, so it cannot show that concussions caused behaviour or mood symptoms; people with worse symptoms may also report more concussions. Concussion totals were self-reported, and the study had no objective record to verify them. The definition used included brief symptoms and “bell rung” or “ding,” without a required symptom duration, and some players reported extreme totals such as 5000 or 16360. The sample was selected from a study of symptomatic former NFL players at high risk for CTE, so it may not represent all former players or other patients. Factor analyses used 85 of the 95 participants because some test data were missing. The reason for the increase after the definition was not established; recall bias, demand characteristics, confabulation, or symptom-related reporting bias could have contributed.

The sample came from the NIH-funded DETECT study. Robert A. Stern received research funding from Avid Radiopharmaceuticals, is a member of the Mackey-White Committee of the NFL Players Association, is a paid consultant to Avanir Pharmaceuticals and Biogen, receives royalties for neuropsychological tests, and receives compensation for expert legal opinion. Robert C. Cantu is a paid consultant to the NFL Head Neck and Spine Committee and NOCSAE, receives book royalties, and receives compensation for expert legal opinion. Christopher Nowinski is president of the Concussion Legacy Foundation, is an unpaid member of the NFL Players Association Mackey-White Committee, has volunteer advisory roles, and receives speaking honoraria and travel reimbursements. Christine Baugh received research funding from the National Collegiate Athletic Association and the Harvard Football Players Health Study, which is funded by the National Football League Players’ Association. The remaining authors declared no conflicts.

Do not treat the post-definition number as a validated count of true concussions. The definition included brief symptoms and “bell rung” or “ding,” some players reported extreme totals, and there was no objective record to verify the reports.