In recent years, more people have been diagnosed with leukemia in town A than in town B. Which of the following study designs would be best suited to determine whether the town location is related to the apparent difference in leukemia incidence in these 2 towns?

Question

In recent years, more people have been diagnosed with leukemia in town A than in town B.  Which of the following study designs would be best suited to determine whether the town location is related to the apparent difference in leukemia incidence in these 2 towns?

Quizplus · Accepted Answer

11ec25c8_d320_ed5d_bc81_351d08e71ca0_MD0003_00 Incidence is defined as the number of new cases of a disease arising in an at-risk population over a specified time period. Subjects without the disease are followed over a period of time to discover how many eventually develop that disease. A cohort study is an observational study in which groups are chosen based upon presence or absence of one or more risk factors. All subjects are observed over time for development of the disease of interest, allowing for estimation of incidence within the total population and comparison of incidences between groups. In this example, the town of residence is the risk factor of interest and leukemia is the disease of interest. Residents of town A and town B could be followed for a period of time and the incidence of leukemia determined for each site. Comparing the incidences between the 2 towns would allow determination of the relative risk for developing leukemia in town A compared to town B. This would be an example of a prospective cohort study; retrospective cohort studies review prior records to determine incidence of a disease of interest in groups of subjects chosen based on presence or absence of a risk factor. (Choice A) In a case-control study, subjects with the disease of interest (cases) are compared to an otherwise similar group of disease-free subjects (controls). Information is then collected about exposure to risk factors. A case-control study is retrospective and meant to determine associations between risk factors and disease occurrence. An odds ratio can be calculated in a case-control study, but the incidence of a disease cannot. (Choice B) A case series is a study involving only patients already diagnosed with a condition of interest. A case series can be helpful in determining the natural history of uncommon conditions, but it provides no information about disease incidence. (Choice C) A clinical trial compares the therapeutic benefit of different interventions in patients already diagnosed with a particular disease. Clinical trials cannot be used to determine disease incidence. (Choice E) In ecological studies, the unit of observation is a population. Disease rates and exposures are measured in 2 (or more) populations, and the association between disease rates and exposures is determined. However, results about associations at the population level may not translate to the individual level. Ecological studies cannot be used to determine incidence. Educational objective: A cohort study design is best for determining the incidence of a disease. Comparing the incidence of the disease in 2 populations, with and without a given risk factor, allows for calculation of relative risk.

In Recent Years, More People Have Been Diagnosed with Leukemia