1. Chronic traumatic encephalopathy, or CTE, is a debilitating brain disorder believed to be caused by repetitive brain trauma. Symptoms include confusion, dementia, memory loss, impulsive behavior, speech impediments, and depression. Dr. Bennet Omalu first noted the presence of CTE during the autopsies two former National Football League (NFL) players. CTE can only be definitively diagnosed after death, and subsequent research was performed by Dr. Ann McKee and colleagues at Boston University on brains donated by families that suspected their loved ones had CTE. Of over 40 brains of former NFL players examined by Dr. McKee, all but one was found to have CTE. Then NFL contends that the research of Drs. Omalu and McKee does not constitute adequate evidence that playing football causes CTE.

a. Explain why the method of data collection could cause selection bias. (2pt)

b. Explain why even if there is an association between playing football and CTE, this is not evidence that CTE is caused by playing football. Give at least one alternate explanation for this association. (2pt)

c. Explain why we cannot perform a randomized control trial to study whether playing football causes CTE. (2pt)

d. What additional data would you collect or analyses would you perform to address the concerns from parts a) and b)? (2pt each)