In a randomized trial, blinding helps reduce bias by concealing allocation from which parties?

• A. Only the participants.
• B. Both participants and researchers.
• C. Only the researchers.
• D. The data analysts.

Answer: (B)

Blinding reduces bias by preventing those involved from knowing which treatment a participant receives. If participants know their allocation, their expectations or beliefs can influence reporting of symptoms, adherence, or perceived improvement. If researchers who interact with participants or assess outcomes know the allocation, their behavior or judgments can unintentionally favor one group, affecting measurements and care. By concealing allocation from both participants and researchers, the trial maintains a fair comparison and minimizes these biases. (Data analysts are sometimes blinded as well in more rigorous designs, but the key protective effect discussed here is against bias from participants and investigators.)