Protocol for an Observational Study on the Effects of Playing High School Football on Later Life Cognitive Functioning and Mental Health

A potential causal relationship between head injuries sustained by NFL players and later-life neurological decline may have broad implications for participants in youth and high school football programs. However, brain trauma risk at the professional level may be different than that at the youth and high school levels and the long-term effects of participation at these levels is as-yet unclear. To investigate the effect of playing high school football on later life depression and cognitive functioning, we propose a retrospective observational study using data from the Wisconsin Longitudinal Study (WLS) of graduates from Wisconsin high schools in 1957. We compare 1,153 high school males who played varsity football to 2,751 male students who did not. 1,951 of the control subjects did not play any sport and the remaining 800 controls played a non-contact sport. We focus on two primary outcomes measured at age 65: a composite cognitive outcome measuring verbal fluency and memory and the modified CES-D depression score. To control for potential confounders we adjust for pre-exposure covariates such as IQ with matching and model-based covariate adjustment. We will conduct an ordered testing procedure that uses all 2,751 controls while controlling for possible unmeasured differences between students who played sports and those who did not. We will quantitatively assess the sensitivity of the results to potential unmeasured confounding. The study will also consider several secondary outcomes of clinical interest such as aggression and heavy drinking. The rich set of pre-exposure variables, relatively unbiased sampling, and longitudinal nature of the WLS dataset make the proposed analysis unique among related studies that rely primarily on convenience samples of football players with reported neurological symptoms.