In 2020, UW Bothell investigators started a study of the association of hypertension and stroke in a group of 2,000 healthy persons who had participated in a hypertension screening program in 2012. The UW Bothell researchers determined exposure categories using blood pressure levels in all persons that were measured at the time of the screening program. A cutoff value of 160 mmhg was used to define “high” blood pressure while those with levels below 160 were identified as having “normal” blood pressure. Using this definition, 1,000 persons had “high” blood pressure levels while the remaining 1,000 persons had “normal” blood pressure. The investigators determined that 150 cases of stroke occurred by the end of 2024, with 113 cases occurring in the hypertensive (high blood pressure) group.

a. What is the study design that the investigators used? (1 point)

b. What type of risk measure should the investigators calculate and why (please provide a detailed explanation)? (2 points)