Which type of clinical study design incorporates both a PLACEBO group and DOUBLE-BLIND methodology?

Correct answer: A. Randomized controlled trial (RCT)

• A. CORRECT — A randomized controlled trial (RCT) with a double-blind, placebo-controlled design is the gold standard. Participants are randomly assigned to treatment or placebo; neither participants nor investigators know the group assignment (double-blind).
• B. INCORRECT — Cross-sectional studies measure exposure and outcome at one point in time; they are observational.
• C. INCORRECT — Cohort studies observe groups over time without placebo or blinding; they are observational.
• D. INCORRECT — Case-control studies look back at exposures in people with and without a disease; they are retrospective and observational.