Answer:
C. 41 %
Explanation:
The proportion of cases of disease X that are due to smoking among those who smoke can be calculated using the formula for attributable risk (AR) among the exposed: AR = (incidence in exposed - incidence in unexposed) / incidence in exposed.
In this case, the incidence in exposed (smokers) is 56/1,000 and the incidence in unexposed (nonsmokers) is 33/1,000. Plugging these values into the formula, we get:
AR = (56/1000 - 33/1000) / (56/1000) = 23/56 ≈ 0.41
So the proportion of cases of disease X that are due to smoking among those who smoke is approximately 41%, which corresponds to answer choice C
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