Officials of a public health department report a higher than normal prevalence of acute myelogenous leukemia (AML) among children age 5-12 in their community. They observe that some households in the community are exposed to chemical waste from a nearby factory and worry that exposure to this waste is responsible for the increased prevalence of AML. A case-control study is designed to evaluate the health department officials' claim that exposure to chemical waste is associated with AML in childhood. Which of the following populations should be selected as the control group?

Question

Officials of a public health department report a higher than normal prevalence of acute myelogenous leukemia (AML) among children age 5-12 in their community.  They observe that some households in the community are exposed to chemical waste from a nearby factory and worry that exposure to this waste is responsible for the increased prevalence of AML.  A case-control study is designed to evaluate the health department officials' claim that exposure to chemical waste is associated with AML in childhood.  Which of the following populations should be selected as the control group?

Quizplus · Accepted Answer

11ec160b_372d_2741_9249_459b36050af2_MD0001_00 A case-control study is the most appropriate study design for evaluating the public health officials' claim. This is because the disease (acute myelogenous leukemia [AML]) is a rare condition occurring at a higher rate in this population, and a retrospective exposure (chemical waste exposure) needs to be evaluated. In case-control studies, 2 groups of subjects are created: cases (subjects with the disease of interest) and controls (subjects without the disease of interest). After the case and control groups are selected, exposure frequency to a specific variable (eg, chemical waste) within both groups is ascertained. If there is a statistically significant difference in exposure frequency between the 2 groups, it is likely that the variable in question is associated with disease development. In this example, AML is the disease of interest; therefore, children with AML should be used as cases and children without AML should be used as controls. Cases and controls should be selected regardless of exposure status to the chemical waste (Choices A and B). Selecting subjects based on exposure status is inappropriate because comparing the frequency of exposure between the case and control groups is what determines whether the exposure is more prevalent among cases as compared to controls. Ideally, exposure frequency among controls should be representative of that among the population of individuals "at risk" of becoming cases. In other words, for a given case-control study, controls are nondiseased individuals who could be considered cases if they had the disease. Often, controls and cases are matched based on independent variables (eg, age, sex) to decrease the effects of confounding. (Choices D, E, and F) AML is the outcome of interest; therefore, children who have AML can be used only to form the cases group and cannot be used as controls. Cases should also be selected regardless of exposure status. Educational objective: Selection of control subjects in case-control studies is intended to provide an accurate estimation of exposure frequency among the nondiseased general population. Cases and controls should be selected based on disease status, not exposure status.

Officials of a Public Health Department Report a Higher Than