What is a double-blind procedure?

• A. An experimental procedure in which neither the participants nor the research staff know which participants are in the experimental or control group; reduces bias.
• B. A method where only the participants don't know their group.
• C. An observational technique with no randomization.
• D. A design where the researchers know who is in which group.

Answer: (A)

Double-blind procedures prevent bias by concealing group assignments from both participants and the researchers who interact with them. In this setup, neither the participants nor the staff know who is receiving the treatment or who is in the control condition, so expectations or cues cannot influence behavior, measurements, or reporting. This reduces placebo effects and observer bias, making the results more trustworthy. If only participants are unaware, that’s single-blind, which still leaves researchers exposed to potential bias. An observational approach with no randomization isn’t about blinding at all, and a design where researchers know the group assignments can introduce bias and contaminate the results.