Which of the following study designs provides the strongest evidence that a new screening test reduces disease-specific mortality at the population level?
- A Prospective cohort comparing screened vs. unscreened individuals
- B Individual randomised controlled trial with mortality as primary endpoint ✓
- C Case-control study nested within a cohort
- D Ecological time-trend analysis
Explanation
The individual-level randomised controlled trial with disease-specific mortality as the primary endpoint is the gold standard for evaluating screening efficacy, as it avoids lead-time bias, length-time bias, overdiagnosis bias, and volunteer bias that afflict observational screening studies. Cohort studies suffer from volunteer bias (healthier people seek screening) and lead-time bias. Case-control and ecological designs are susceptible to multiple additional biases. The RCT's random allocation ensures that screened and unscreened groups differ only by the screening itself.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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