What is the main purpose of blinding in clinical trials?

• A. To speed recruitment
• B. To reduce bias by concealing treatment allocation
• C. To ensure randomization
• D. To guarantee treatment efficacy

Answer: (B)

Blinding is about preventing knowledge of which treatment a participant or investigator has from influencing behavior, care, or outcomes. When people know they’re on a particular treatment, their expectations can shape how they report symptoms or how outcomes are rated, creating bias in the results. By concealing allocation, you reduce placebo and nocebo effects in participants, avoid differential care by clinicians, and minimize biased outcome assessment. This protection is especially important for subjective outcomes like pain or quality of life, though it helps with the overall credibility of the findings. Blinding isn’t about speeding up recruitment, and it doesn’t by itself ensure randomization or guarantee that a treatment is effective—the aim is to keep the comparison fair so observed effects more accurately reflect true differences rather than expectations.