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Difficulty: HardEpidemiologic Study Designs

An occupational medicine physician is investigating the long-term respiratory effects of a synthetic resin used in a large manufacturing plant. The physician accesses company employment records and identifies 300 workers who were exclusively assigned to the resin-mixing department between 2010 and 2015. Additionally, 300 workers who were exclusively assigned to the packaging department, where the resin is never handled, are identified from the same time period. The physician then reviews the annual employee health clinic records and spirometry logs from 2015 through 2025 for all 600 workers to determine the incidence of newly diagnosed asthma. Which of the following best describes this study design and the most appropriate primary measure of association to calculate?

  1. Retrospective cohort study; relative riskAnswer
  2. B
    Retrospective cohort study; odds ratio
  3. C
    Case-control study; odds ratio
  4. D
    Case-control study; relative risk
  5. E
    Cross-sectional study; prevalence ratio

Answer

Retrospective cohort study; relative risk
The correct answer identifies this as a retrospective cohort study using relative risk. A retrospective cohort study identifies subjects based on their past exposure status (in this case, resin-mixing vs. packaging) and then looks forward in time (using historical records from 2015-2025) to determine the incidence of the outcome (asthma). Because this design tracks populations over time to measure the true incidence of disease, the relative risk (or risk ratio) is the most appropriate primary measure of association.

Step-by-Step Solution

1
Analyze how the study groups were initially formed.
Workers were selected based on their department assignment between 2010 and 2015, meaning they were grouped by their exposure status (resin-mixing vs. packaging).
Identifying the initial grouping method is the critical first step in distinguishing between cohort and case-control designs.
2
Determine the direction of the study timeline.
The investigator looked forward from the time of exposure to assess the future development (incidence) of asthma between 2015 and 2025.
Tracking populations from exposure to outcome defines a cohort study. Because all events (exposure and outcome) had already occurred at the time the study was initiated, it is a retrospective cohort study.
3
Select the appropriate measure of association for the identified design.
Because this is a cohort study measuring incidence, relative risk (risk ratio) is the correct primary measure.
Relative risk compares the incidence of disease in the exposed group to the incidence in the unexposed group, which can be directly calculated in a cohort study.

Key Concept

Retrospective cohort studies group participants by past exposure status and track them over time to determine outcome incidence, utilizing relative risk as the primary measure of association.
Estimated Time:1m 15s
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Topics

Epidemiologic Study Designs

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