Question

A cohort study was undertaken to examine the association between high lipid level and coronary heart disease. Participants were classified as having either a high lipid level (exposed) or a low or normal lipid level (unexposed). Because age is associated with both lipid level and risk of heart disease, age was considered a potential confounder, and the age of each subject was recorded. The following data describes the study participants:

                          Developed CHD No CHD
EXPOSED (High lipid level)
                  young       20        3980
                    old         200        5800

UNEXPOSED (Low or normal lipid level)
                  young       18         6982
                     old          65        2935

a. Calculate AND interpret the appropriate crude ratio measure of association combining the data for young and old individuals

Answer 1

For young,

for high lipid level, 20 had CHD 3980 didn't have CHD.

So, the ratio is 1:199

1 = CHD

199 = No CHD

For old,

for high lipid level, 200 had CHD 5800 didn't have CHD.

So, the ratio is 1:29

1 = CHD

29 = No CHD

For young,

for normal-low lipid level, 18 had CHD 6982 didn't have CHD.

So, the ratio is 1:388

1 = CHD

388 = No CHD

For old,

for high lipid level, 65 had CHD 2935 didn't have CHD.

So, the ratio is 1:45

1 = CHD

45 = No CHD

Interpretation: According to the crude ratio, it is predictable that old person are always more susceptible to CHD compared to young. When lipid level is high, older people are more susceptible, but due to their age, they can have CHD, even when they have low lipid level. Younger people are always less susceptible.