Answer to Question 1
Ans: D
Feedback:
Relative risk (RR) is defined as the ratio of disease incidence (or death) in an exposed population to that in an unexposed population. The assumption is that the underlying risk without the exposure is the same in both groups. Relative risk is a ratio ranging from 0 to infinity that indicates the strength of the association between the risk factor and the outcome. It is calculated by dividing the risk in the group exposed to a risk factor by the risk in the unexposed group. In this case, we perform the following calculation: 735/245 = 3. An RR significantly greater than 1 (statistically) indicates that the exposure is associated with increased risk of disease. An RR significantly less than 1 (statistically) indicates that the exposure is associated with decreased risk of disease; that is, the exposure is protective. An RR not significantly different from 1 (statistically) indicates that there is no association between the exposure and the risk of disease.
Answer to Question 2
Ans: A, C, E
Feedback:
Case-control studies have several advantages: they allow for the examination of multiple exposures for a single outcome, are suitable for studying rare diseases and those with long latency periods, require fewer case-subjects, and generally are quicker and less expensive to conduct than cohort studies, making them well suited for an outbreak investigation. They have several disadvantages: they are not appropriate for studying rare exposures, they are subject to bias because of the method used to select controls, and they do not allow the direct measure of the incidence of disease.