Common RCT Designs
Parallel-Group Trial
- Participants remain in one assigned group throughout the study.
- Most common design.
Crossover Trial
- Each participant receives both interventions in sequence.
- Each participant serves as their own control.
- Requires a washout period.
- Appropriate for stable chronic conditions.
- Avoid when:
- Disease changes rapidly
- Treatment has permanent effects
- Carryover effects are likely
Factorial Trial
- Tests ≥2 interventions simultaneously.
- Example: drug A/placebo combined with drug B/placebo.
Cluster-Randomized Trial
- Randomizes groups, eg, clinics or communities.
- Useful when individual randomization would cause contamination.
- Analysis must account for correlation among people within each cluster.