Interim analysis and early stopping are used to compare treatment arms with respect to what?

• A. Endpoint definitions
• B. Efficacy or safety
• C. Economic cost
• D. Recruitment speed

Answer: (B)

Interim analysis and early stopping focus on monitoring trial data to detect a true difference between treatment arms early, so a trial can stop if there is clear benefit, unexpected harm, or futility. This is why they are used to compare the arms with respect to efficacy outcomes and adverse events. They are not about redefining how endpoints are measured, nor about costs or recruitment speed, though those factors can influence design decisions. In practice, stopping for efficacy might be triggered by a strong improvement in outcomes, while stopping for safety would occur if adverse events are more frequent or severe in one arm.