In a closed cohort study that included 2,000 males age 40-59 years, 400 had initial serum cholesterol levels of
less than 220 mg %, 900 had levels of 220-270 mg % and 700 had levels greater than 270 mg %. Among these three cholesterol classes: (1) less than 220; (2) 220-270; and (3) greater than 270, the number of new cases of coronary heart disease during the first year of follow-up were 3, 12, and 14 respectively.
A. What was the incidence of coronary heart disease within each of the three cholesterol classes? (assume complete follow-up).