It is estimated that the prevalence of smoking in a population is 50%. A cohort study conducted using a random sample from this population showed that the 5-year risk of ischemic stroke is 1:1000 among smokers and 0.5:1000 among non-smokers. What percentage of ischemic strokes observed in smokers can be attributed to their smoking status?
A)10%
B)25%
C)33%
D)50%
E)75%

Question

It is estimated that the prevalence of smoking in a population is 50%.  A cohort study conducted using a random sample from this population showed that the 5-year risk of ischemic stroke is 1:1000 among smokers and 0.5:1000 among non-smokers. What percentage of ischemic strokes observed in smokers can be attributed to their smoking status?
A)10%
B)25%
C)33%
D)50%
E)75%

Quizplus · Accepted Answer

Explanation: In this scenario, the attributable risk percent (ARP) should be calculated. ARP is a measure of excess risk and estimates the proportion of disease among exposed subjects that is attributed to exposure status. Two approaches can be used to calculate ARP. The first uses the following formula: ARP = (Risk in exposed - Risk in unexposed) / Risk in exposed = (0.1 - 0.05) / 0.1 = 0.5 (50%). The second uses relative risk (RR): ARP = (RR - 1) / RR = (2 - 1) / 2 = 0.5 (50%). As a result, 50% of the ischemic strokes observed in smokers can be attributed to their smoking status and could therefore have been eliminated if these individuals had not smoked. Educational objective: The attributable risk percent (ARP) is a measure of excess risk. It estimates the proportion of the disease in exposed subjects that is attributed to exposure status. ARP = (Risk in exposed - Risk in unexposed) / Risk in exposed.

It Is Estimated That the Prevalence of Smoking in a Population