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Difficulty: EasyEpidemiologic Study Designs

A medical researcher is evaluating the association between a particular occupational chemical exposure and the development of bladder cancer. Using historical records from a large manufacturing company spanning the past 20 years, the researcher identifies 2,000 employees who worked in the chemical processing division (exposed) and 2,000 employees who worked in the administrative division (unexposed). He then examines the employees' health insurance claims over the subsequent two decades to determine the number of newly diagnosed bladder cancer cases in each group. Which of the following best describes this epidemiologic study design?

  1. Retrospective cohort studyAnswer
  2. B
    Case-control study
  3. C
    Prospective cohort study
  4. D
    Cross-sectional study
  5. E
    Randomized controlled trial

Answer

The correct answer is a retrospective cohort study, because participants are initially categorized by their past exposure status and then followed longitudinally using historical records to assess the development of the outcome.
The described study is a retrospective cohort study. In any cohort study, the investigator categorizes participants based on their exposure status (in this case, chemical exposure vs. no chemical exposure) and then assesses the incidence of the outcome (bladder cancer) over time. It is considered 'retrospective' because the investigator uses historical records to establish both the past exposure and the subsequent outcome, rather than following patients in real-time into the future.

Step-by-Step Solution

1
Identify the primary grouping criterion used to select the study participants.
Participants were selected and grouped based on whether they worked in the chemical processing division (exposed) or the administrative division (unexposed).
Grouping by exposure status is the defining characteristic of a cohort study, whereas grouping by outcome status characterizes a case-control study.
2
Determine the temporal relationship and data collection timeframe of the study.
The researcher uses historical records from the past 20 years for both the initial exposure categorization and the subsequent development of bladder cancer.
Because the cohort is identified from past records and followed forward using historical data (both exposure and outcome have already occurred), the cohort study is retrospective rather than prospective.
3
Synthesize these findings to classify the study design.
The combination of grouping by exposure and using entirely historical data to track outcomes defines a retrospective cohort study.
This confirms the correct epidemiologic terminology for the described methodology.

Key Concept

Epidemiologic Study Designs
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Epidemiologic Study Designs

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