Intention-to-treat analysis quantifies which concept in clinical trials?

• A. Efficacy
• B. Effectiveness
• C. Adherence
• D. Sample size adequacy

Answer: (B)

Intention-to-treat analysis measures effectiveness. By analyzing participants in the groups to which they were originally randomized, regardless of whether they actually received or adhered to the assigned treatment, this approach reflects the real-world impact of offering the therapy, including nonadherence, crossovers, and dropouts. It preserves randomization and tends to show what happens when treatment is offered in practice. This is different from efficacy, which assesses the effect under ideal conditions with full adherence (often via per-protocol analyses). Adherence is about how well participants follow the protocol, not the overall treatment effect under assignment, and sample size adequacy relates to statistical power, not the effect estimated by ITT.