A randomized controlled trial analyzes all participants according to the arm to which they were originally allocated, regardless of adherence, crossovers, or protocol deviations. The principal advantage of this intention-to-treat approach is that it:

• A Increases the statistical power of the comparison
• B Removes the need for allocation concealment
• C Provides the true biological efficacy of the drug under ideal conditions
• D Preserves the benefits of randomization and avoids bias from differential adherence and withdrawal ✓

Explanation

Intention-to-treat analysis keeps the groups comparable in all baseline characteristics, including prognosis, because everyone randomized stays in their assigned group. If non-adherent or withdrawn patients are excluded differently across arms, the balance created by randomization breaks down and bias enters. It answers the practical question of effectiveness rather than efficacy, so option C describes per-protocol analysis instead. Intention-to-treat usually dilutes the measured effect and thus reduces apparent power, making option A incorrect.

Reference: Gordis Epidemiology, 6th ed.

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