Discover why cohort studies are more efficient for investigating rare exposures like asbestos or radiation, requiring smaller sample sizes compared to case-control designs.
Table of Contents
Question
Select the study design that will require smaller sample size when the exposure is rare; for example an occupational exposure (e.g. asbestos, radiation, and pesticides).
A. Case-control
B. Cohort
Answer
B. Cohort
Explanation
Cohort studies are more efficient for studying rare exposures by directly following a group over time to see who develops the disease.
Cohort studies are the optimal choice when studying rare exposures such as occupational hazards (e.g., asbestos, pesticides). Here’s why:
Key Explanation
Cohort Studies Prioritize Exposure Status
Cohort studies start by identifying individuals based on their exposure status (exposed vs. unexposed) and follow them over time to observe outcomes.
If the exposure is rare, researchers can intentionally recruit a sufficient number of exposed individuals (e.g., workers in high-risk industries), ensuring statistical power without requiring an excessively large sample.
Case-Control Studies Struggle with Rare Exposures
Case-control studies begin with individuals who already have the outcome (cases) and compare their exposure history to controls without the outcome.
If the exposure is rare, even among cases, there may be too few exposed individuals to detect meaningful associations, necessitating a larger sample size to achieve significance.
Efficiency of Cohort Designs
Cohort studies directly calculate incidence rates and relative risks, making them more statistically robust for rare exposures.
Retrospective cohort studies further reduce logistical challenges by using historical data, combining cost-effectiveness with the ability to study rare exposures.
Why Not Case-Control?
While case-control studies excel for rare outcomes, they are inefficient for rare exposures because they rely on retrospectively identifying exposures within a limited pool of cases and controls.
Cohort studies are better suited for rare exposures, as they allow targeted enrollment of exposed individuals, ensuring adequate sample efficiency. Case-control studies, by contrast, risk underpowered results unless the outcome itself is rare.
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