Which statement correctly describes a double-blind study?

• A. Participants know treatment; researchers know
• B. Participants know; researchers don't know
• C. Neither participants nor researchers know
• D. Only the sponsor knows

Answer: (C)

The main idea here is that a double-blind study keeps both participants and researchers in the dark about who gets the experimental treatment and who gets the comparator. This design reduces bias from expectations—patients’ reports and clinicians’ assessments are less likely to be influenced by knowing the treatment, which helps ensure the outcomes reflect the true effect of the intervention rather than placebo effects or observer bias. In practice, assignments are randomized and concealed, often with identical-looking treatments and a code kept by an independent party until analysis. For example, in a drug trial, neither the patient nor the clinician knows who receives the active drug versus a placebo. The other scenarios would leak information that could bias results: if participants know their treatment, their responses may change; if researchers know, their assessments or care could be biased; and if only the sponsor knows, blinding is lost and objectivity is compromised.