A group of researchers conducted a study to identify risk factors for death after coronary artery bypass graft (CABG) surgery. Individuals who had undergone CABG and who are enrolled in a cohort study represent the source population for the new study. A random sample of 150 of these individuals was selected; they were initially classified as diseased (dead) or nondiseased (alive) based on death following CABG. Diseased and nondiseased subjects were matched for age and gender. The frequency of several risk factors was subsequently compared between the diseased and nondiseased groups. Study results showed that diabetes, cigarette smoking, peripheral vascular disease, lengthy hospitalization, and elevated triglycerides, total cholesterol, C-reactive protein, and high-density lipoprotein cholesterol were significantly associated with death following CABG. Which of the following best describes the study design?
A)Observational case series
B)Nested case-control
C)Prospective cohort
D)"Snapshot" cross-sectional
E)Experimental crossover

Question

A group of researchers conducted a study to identify risk factors for death after coronary artery bypass graft (CABG) surgery.  Individuals who had undergone CABG and who are enrolled in a cohort study represent the source population for the new study.  A random sample of 150 of these individuals was selected; they were initially classified as diseased (dead) or nondiseased (alive) based on death following CABG.  Diseased and nondiseased subjects were matched for age and gender.  The frequency of several risk factors was subsequently compared between the diseased and nondiseased groups.  Study results showed that diabetes, cigarette smoking, peripheral vascular disease, lengthy hospitalization, and elevated triglycerides, total cholesterol, C-reactive protein, and high-density lipoprotein cholesterol were significantly associated with death following CABG.  Which of the following best describes the study design?
A)Observational case series
B)Nested case-control
C)Prospective cohort
D)"Snapshot" cross-sectional
E)Experimental crossover

Quizplus · Accepted Answer

Explanation: 11ec2b69_c108_26b3_8f63_d5c67b818660_MD0005_00 In this study, individuals who underwent coronary artery bypass graft (CABG) surgery were randomly selected from subjects enrolled in a cohort study. Individuals were initially identified based on disease status (ie, cases: those with CABG who died during the cohort study; controls: those with CABG who survived during the same period). The frequency of exposure to risk factors (eg, diabetes) was subsequently compared between cases and controls. Therefore, this is a case-control study. This type of case-control study, which draws its cases and controls from a group of individuals participating in a follow-up study (ie, cohort or experimental) is known as a nested case-control study. Participants who develop the outcome of interest (eg, post-CABG death) during a cohort study become cases in a nested case-control study whereas participants who do not develop the outcome (eg, post-CABG survival) serve as controls. Risk factors associated with the outcome can then be investigated. (Choice A) In a case series, a small group of individuals with a similar diagnosis or treatment is described at a point in time or followed over time. It is an observational study but has no comparison group, so it cannot establish associations between risk factors and disease. In contrast, the case-control study described above has a comparison group and an implicit purpose to evaluate associations between exposures (eg, diabetes) and disease (ie, post-CABG death). (Choice C) In a cohort study, individuals are initially identified based on their exposure status (eg, with or without diabetes); they are then followed over time to assess development of an outcome of interest (eg, post-CABG death). In the study described above, individuals were initially identified as cases or controls based on their outcome status (ie, died or survived following CABG) and subsequently assessed for past exposure to ≥1 risk factors (eg, diabetes). (Choice D) In a cross-sectional study, a snapshot (ie, assessment of a defined population at a particular time) is used to estimate the prevalence of risk factors and disease simultaneously. In contrast, individuals in a case-control study are initially identified based on disease status. (Choice E) In a crossover (experimental) study, individuals are exposed to different treatments or exposures sequentially. In the case-control study, individuals were enrolled in an observational follow-up study, not in an experimental study. Educational objective: A nested case-control study is an observational study in which subsets of cases and controls identified and selected from a follow-up study (eg, cohort, experimental) are compared with regard to the distribution of risk factors.

A Group of Researchers Conducted a Study to Identify Risk