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Question 3#

Over the last 10 years, more people in the town of Nankville appear to be suffering from Hodgkin lymphoma than in the town of Gridora.

Which of the following types of studies is best for calculating the difference in incidence between Nankville and Gridora?

A. Cross-sectional
B. Case-control
C. Cohort
D. Clinical trial

Correct Answer is C


Cohort. In this question, we need to find the study that is best for calculating the incidence (the frequency of new cases of a particular disease that arise in a population at risk over a certain time period). One can infer that in order to figure out the incidence, people without the disease need to be followed over a certain time period to determine how many of them develop that disease of interest. The best choice is a cohort study, a prospective observational study. Once residents in Nankville and Gridora have been followed over a certain time period, the incidence of Hodgkin lymphoma can be determined. Furthermore, the comparison of incidences will allow one to calculate the relative risk for developing Hodgkin lymphoma in one town versus the other. (B) Case-control is retrospective and patients with the disease (cases) are compared to patients without the disease (controls). Information is collected about previous exposure to risk factors. Case-control studies allow for calculation of odds ratio, but not incidence. (A) Cross-sectional studies are studies at one point in time, so these studies are ideal for measuring a disease’s prevalence (total number of cases in a population). (D) Clinical trials are used to determine the benefit of an intervention (drug, procedure, etc.) in patients who already have the disease. They do not determine incidence.