A retrospective cohort study is conducted of the relationship between the use of

ID: 3125802 • Letter: A

Question

A retrospective cohort study is conducted of the relationship between the use of estrogen and coronary heart disease. A total of 5000 exposed and 5000 unexposed women are enrolled and followed for 15 years for the development of myocardial infection. A total of 200 estrogen users developed the outcome compared with 300 myocardial infarctions among the nonusers.

A. What is the risk of a myocardial infarction among estrogen users?

B. What is the risk of a MI among nonusers of estrogen?

C. What is the risk ratio of a MI?

Please show your work. THANKS!

Explanation / Answer

Exposed

Unexposed

200

300

500

No MI

4800

4700

9500

5000

10000

A. What is the risk of a myocardial infarction among estrogen users?

Risk=200/5000 =0.04

B. What is the risk of a MI among nonusers of estrogen?

Risk=300/5000 =0.06

C. What is the risk ratio of a MI?

Risk ratio =0.04/0.06 =0.667

A risk ratio < 1 suggests a reduced risk in the exposed group