Suppose that a cohort study of body mass index and coronary heart disease (CHD) was undertaken. Participants were classified as having either a high or normal body mass index. Because age is associated with both body mass index and risk of CHD, age was considered a potential confounder and the age of each participant was recorded. The following data were gathered from the study participants:

Normal Body Mass IndexHigh Body Mass Index

DISEASEAGEDISEASEAGE
STATUSYoungOldSTATUSYoungOld

Developed1865Developed20200
CHDCHD

Did Not69822982Did Not39805800
Develop CHDDevelop CHD

Total70003000Total40006000

1) Set up the two by two to evaluate the crude association between body mass index and CHD and calculate the crude risk ratio?

2) Set up the two by two tables to evaluate the relationship between body mass index and CHD stratified by age. That is, calculate the risk ratios separately for the young and old participants?

3)Is age a confounder in this study? How do you know?