In 2002, investigators started a study of the association of cholesterol levels and stroke in a group of 2000 healthy persons who had participated in a cholesterol screening program in 1992. The investigators determined exposure categories using cholesterol levels in all persons that were measured at the time of the screening program. A cut-off value of 200 mg/dl was used to define "high" cholesterol while those with levels below 200 were identified as having "low" cholesterol. Using this definition, 1000 persons had "high" cholesterol levels while the remaining 1000 persons had "low" cholesterol. The investigators deternined that 150 cases of stroke occured by the end of 2004, with 113 cases occurring in the high cholesterol group.

Question: Using the reported data, what is the estimate of the risk measure that was chosen?

2. What is the study design that the investigators used?

3, What type of risk measure should the investigator calculate?