2 Possible versions of control in a study of football and dementia There is evidence that severe repeated head trauma accelerates the on-set of cognitive decline or dementia (Graves et al. 1990, Mortimer et al. 1991), with specific concern about the risks faced by professional football players and boxers (McKee et al. 2009, Lehman et al. 2012). It is unclear whether there is also increased risk from playing football on a team in high school, but there have been several recommendations against tackle football in high school (Bachynski 2016, Miles and Prasad 2016). Does high school football accelerate the on-set of cognitive decline? A recent investigation used data from the Wisconsin Longitudinal Study, comparing cognition and mental health measured at age 65 and 72, recorded in 2005 and 2011, of men who played football on a high school team in the mid 1950’s to male controls of similar age who did not play football (Deshpande et al. 2017). Following the practice in clinical trials, and as is recommended for observational studies by Rubin (2007), the design and protocol for this study were published on-line after matching was completed but before outcomes were examined (Deshpande et al. 2016, arXiv preprint arXiv:1607.01756 ). The small number of people who engaged in sports other than football with high incidences of head trauma such as soccer, hockey, and wrestling were excluded from both the football and control groups. One outcome was the 0-10 score on a ten item delayed word recall (DWR) test at ages 65 and 72. The delayed word recall test was designed as an inexpensive measure of memory loss associated with dementia; see Knopman and Ryberg (1989). In this test, a person is asked to remember a list of words that is then read to the person. Attention then shifts to another activity, and after a delay, the person is asked to recall as many words from the list as possible. The DWR score is the number of words remembered. On average, in the Wisconsin Longitudinal Study, performance on the delayed word recall test declined by half a word from age 65 to age 72. It is useful to keep that half-word, 5