This lecture comes from Yale's online course Understanding Medical Research: Your Facebook Friend is Wrong, which teaches viewers how to evaluate health claims they encounter in the news and on social media. In this session the instructor explains the randomized controlled trial, the design researchers treat as the gold standard for testing whether a treatment actually works. The talk covers why random assignment matters, how it guards against bias and confounding variables that plague observational studies, and what blinding adds when done well. Examples show how a poorly designed trial can produce misleading results even when the statistics look sound. Aimed at a general audience rather than statisticians, the lecture builds the vocabulary needed to read a clinical trial report critically, whether reported in a journal or repeated secondhand in a friend's post.