You are investigating the role of physical activity in heart disease and suggest that physical activity protects against having a heart attack. while presenting these data to your colleagues, someone asks if you have thought about confounders such as factor x. this factor x could have confounded your interpretation of the data if it: a. is a factor for some other disease, but not heart disease. b. is a factor associated with physical activity and heart disease. c. is a part of the pathway by which physical activity affects heart disease. d. has caused a lack of follow-up of test subjects.

Adouble-blinded trial for a new indication is conducted under an ind comparing two (2) marketed drugs, at twice the approved prescribed doses. on day 2, subject 603 had difficulty breathing. although it was life-threatening initially, subject 603 was treated and discharged directly from the emergency department after complete recovery. on day 5, subject 20 had a headache, which led to hospitalization and required blood pressure lowering medications. these episodes cannot be explained on the basis of the pharmacological property of either drug or the subjects' medical histories. the investigator would submit an sae report for