A researcher investigates a new vaccine by randomly assigning 10 villages to vaccination and 10 to control, but treating all individuals within each village as one unit. This design is called a:
- A Community trial (randomized controlled field trial)
- B Stepped-wedge trial
- C Cluster randomized trial (CRT) ✓
- D Factorial trial
Explanation
A Cluster Randomized Trial (CRT) randomizes groups (clusters) — here villages — rather than individuals. All members within a cluster receive the same intervention. CRTs are used when individual randomization is impractical (vaccine herd immunity, community-level interventions) or to avoid contamination between groups. The key statistical consequence is intracluster correlation coefficient (ICC) — individuals within a cluster are more similar than those between clusters. Sample size must be inflated by the design effect (DEFF = 1 + [m-1] × ICC, where m = cluster size). A community trial is a broader term; a CRT is the specific design described.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.