Use the scenario to answer the following questions:

A cohort study was undertaken to examine the association between high blood pressure and coronary heart disease (CHD). Participants were classified as having either a high blood pressure (exposed) or a low/normal blood pressure (unexposed). Because age is associated with both blood pressure and risk of heart disease, age was considered a potential confounder or effect modifier, and the age of each subject was recorded. The following data describes the study participants: Overall, there were 9,000 young participants and 11,000 old participants. Of the 4,000 young participants with high blood pressure, 25 of them developed CHD. Of the 6,000 old participants with high blood pressure, 200 of them developed CHD. In the unexposed, 15 young and 70 old participants developed CHD.

Question 26

Complete the 2x2 table for crude data based on the information given above. What are the values for A, B, and C?

		CHD	No CHD	Total
High Blood Pressure	Yes	A	9,775	10,000
No	B	9,915	10,000
	Total	C	19,690	20,000

Choice 1. A: 25, B: 15, C: 40

Choice 2. A: 200, B: 70, C: 270

Choice 3. A: 225, B: 85, C: 310

Choice 4. A: 215, B: 95, C: 310

Question 27

What is the appropriate crude ratio measure of association for this study?

a. Odds ratio

b. Risk ratio (relative risk)

c. Risk difference

d. Attributable risk

Question 28

Calculate the appropriate crude ratio measure of association. What is the value?

a. 1.67

b. 2.11

c. 2.65

d. 2.86

Question 29

Based on data from the age-stratified tables below, what is the risk ratio (relative risk) for young people and old people?

YOUNG
		CHD	No CHD	Total
High Blood Pressure	Yes	25	3,775	4,000
No	15	4,985	5,000
	Total	40	8,760	9,000

OLD
		CHD	No CHD	Total
High Blood Pressure	Yes	200	5,800	6,000
No	70	4,930	5,000
	Total	270	10,730	11,000

a. Young: RR = 1.48, Old: RR = 1.82

b. Young: RR = 2.08, Old: RR = 2.36

c. Young: RR = 2.80, Old: RR = 2.63

Question 30

Do the data provide evidence of effect modification based on the ratio scale?

a. Yes

b. No