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Difficulty: MediumEpidemiologic Study Designs

A pharmacovigilance team utilizes a nationwide electronic health record (EHR) database to evaluate the risk of acute kidney injury (AKI) associated with a novel broad-spectrum antibiotic. The researchers identify all adult patients in the database who were prescribed the novel antibiotic between January 2020 and December 2024. They also identify a comparison group of adults who were prescribed a standard alternative antibiotic during the same timeframe. The researchers then analyze the longitudinal EHR data through December 2025 to determine the incidence of AKI in both groups. Which of the following statements regarding this study design are correct?

  1. Participants are initially categorized according to their exposure status prior to evaluating the occurrence of the outcome.Answer
  2. The study design permits the direct calculation of disease incidence and relative risk.Answer
  3. C
    This methodology represents a case-control design because the researchers are analyzing historical data after the outcomes have already occurred.
  4. D
    If stratifying the analysis by baseline chronic kidney disease status shows a strong association in patients with the disease but no association in healthy patients, then chronic kidney disease is acting as a confounding variable.
  5. E
    The design is considered cross-sectional because the investigators extracted all electronic health record data simultaneously at the end of the study period.

Answer

The correct statements are that participants are initially categorized according to their exposure status prior to evaluating the occurrence of the outcome, and that the study design permits the direct calculation of disease incidence and relative risk.
The scenario describes a retrospective cohort study because the investigators define groups based on their exposure (type of antibiotic) using historical data, and then follow their records over time to see who develops the outcome (AKI). All cohort studies—whether prospective or retrospective—allow investigators to directly measure the incidence of disease because they start with a population at risk. With incidence known, researchers can directly calculate relative risk.

Step-by-Step Solution

1
Identify the primary study design based on the methodology described in the stem.
The researchers grouped patients based on past exposure (novel vs. standard antibiotic) and tracked their records forward in time to observe an outcome (AKI). This is a retrospective cohort study.
Correctly identifying the study architecture is essential for determining its properties, strengths, and limitations.
2
Evaluate the capabilities and characteristics of a retrospective cohort study.
Because cohort studies track a defined population at risk over time, they allow for the direct measurement of disease incidence, which in turn allows for the calculation of relative risk.
Differentiating what statistical measures are appropriate for specific designs (e.g., relative risk for cohorts vs. odds ratios for case-control studies) is a core epidemiological concept.
3
Analyze the incorrect statements to distinguish related epidemiological concepts.
The study is not a case-control study (which groups by outcome) or a cross-sectional study (which lacks a longitudinal timeframe). Furthermore, a variable that causes an association to differ across strata is an effect modifier, not a confounder.
Testing common cognitive pitfalls ensures a robust understanding of study methodology.

Key Concept

Identifying a retrospective cohort study and understanding its defining characteristics, such as grouping by exposure to calculate disease incidence and relative risk.
Estimated Time:1m 15s
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Epidemiologic Study Designs

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