Phase 3 trial sample size typically ranges from:

• A. 50-100
• B. 20-80
• C. 100-300
• D. 1000-3000

Answer: (D)

Phase 3 trials are large-scale confirmatory studies designed to verify a treatment’s efficacy and monitor safety across a broad, diverse patient population. To reliably detect meaningful differences between the new treatment and standard care, and to catch rar or less common adverse events, these trials require enough participants to achieve adequate statistical power. About 1,000 to 3,000 participants is a typical range for this purpose, providing enough data to generalize results and support regulatory decisions.

Smaller numbers, like those in early-phase studies, are generally used to explore dosing, safety signals, and feasibility, not to provide definitive efficacy conclusions. Therefore, the 1,000–3,000 range best fits what phase 3 trials aim to achieve.