Question

The death rate per 100,000 for lung cancer is 7 among non-smokers and 71 among smokers. The death rate per 100,000 for coronary thrombosis is 422 among non-smokers and 599 among smokers. The prevalence of smoking in the population is 55%. Among smokers, the etiologic fraction of disease due to smoking is:

A.

cannot be determined from the information provided.

B.

0.90 for lung cancer and 0.88 for coronary thrombosis.

C.

0.90 for lung cancer and 0.29 for coronary thrombosis.

D.

0.89 for lung cancer and 0.88 for coronary thrombosis.

E.

0.89 for lung cancer and 0.29 for coronary thrombosis.

Answer 1

Answer - option c - 0.90 for lung cancer and 0.29 for coronary thrombosis.

Explanation - The fraction of population etiologic (PAF) is - Pe (RRe - 1) / [ 1 + Pe ( RRe - 1)]

the value of Pe is the prevalence of the risk exposed and the value of RRe is the relative risk of the disease due to the risk exposure.
in the provided case, the value of Pe is 0.55

in the given case, RRe = number of events when exposed / number of events when not exposed.
therefore, the calculation of RRe will be - 71/7= 10.1

PAF for the cancer of lungs will be = 0.55 ( 10.1-1) / ( 1+ 0.55 (10.1-1)) = 0.55 x 9.1 / 1 + 0.55 x 9.1

= 5.005 /6.005 = 0.83

Similarly, the value of RRe for the case of coronary thrombosis would be =

0.55 (1.419 - 1) / (1+ 0.55 (1.419-1)) = 0.55 x 0.419 / 1+0.55x 0.419= 0.23045 / 1.23045 = 0.18

Therefore, PEF of the disease because of smoking is 0.83. And for the occurrence of coronary thrombosis is 0.18.

Solution - The etiologic fraction of the lung cancer is = 71-7 / 71 = 64/71 = 0.90

and the etiologic fraction for the coronary thrombosis is = 599-422 / 599

= 177 / 599= 0.29

Therefore, among smokers the etiologic fraction of disease due to smoking habit is 0.90 for occurrence of lung cancer and for occurrence of coronary thrombosis is 0.29.