This lecture opens Yale's course on evaluating medical claims, part of a series subtitled 'Understanding Medical Research: Your Facebook Friend is Wrong.' The instructor lays out the basic architecture of scientific research: how a question becomes a hypothesis, how studies are designed to test it, and how results move from a lab or a clinical trial into a published paper. The lecture walks through the difference between observational studies and randomized controlled trials, explaining why one type of evidence carries more weight than another when a headline claims a food or drug causes some outcome. It sets up the tools a viewer needs before they can judge a study's quality: sample size, control groups, and the basic logic of statistical inference. Eighteen minutes of groundwork meant to make the rest of the course, and any medical claim shared online, easier to evaluate critically.