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 is the relative risk of ischemic stroke among smokers compared to non-smokers?
A)0)5
B)1)0
C)2)0
D)2)5
E)5)0

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 is the relative risk of ischemic stroke among smokers compared to non-smokers?
A)0)5
B)1)0
C)2)0
D)2)5
E)5)0

Quizplus · Accepted Answer

Explanation: Relative risk (RR) represents a measure of outcome in follow-up studies. It is a risk ratio comparing risk of an outcome among the exposed to that among the unexposed. In this case, the 5-year risk of ischemic stroke among the exposed (smokers) group is 0.1% (1:1000), and the risk among the unexposed group is 0.05% (0.5:1000). As a result, the RR = 0.1/0.05 = 2.0. The 5-year risk of ischemic stroke in smokers is twice that of non-smokers. Educational objective: Relative risk is a measure of outcome in follow-up studies. It is the risk of the exposed group divided by the risk of the unexposed group.

It Is Estimated That the Prevalence of Smoking in a Population