Research & evidence
How to read medical research: the evidence pyramid, study types, correlation versus causation, clinical trial phases, risk numbers and how to judge health news — plus two tools to check a study and find recruiting trials.
How medical knowledge is built
- The evidence pyramid Not all medical studies are equally able to answer “does this treatment work?”. The evidence pyramid is a simplified teaching tool that orders study types: systematic reviews that pool many studies at the top, then randomized controlled trials, then observational studies, and early signals such as case reports and lab or animal research at the base.Editorially complete
- Types of medical studies Studies in people fall into two broad groups: experimental studies, where researchers decide who receives a treatment or intervention (such as clinical trials), and observational studies, where researchers only observe what happens. Each answers some questions well and has clear limits.Editorially complete
- Phases of clinical trials Before a new medicine or treatment reaches the public it passes through a series of trials in volunteers, called phases. Each phase answers different questions: safety first, then effectiveness, then comparison with existing treatments in large groups, then monitoring after approval.Editorially complete
- Peer review, preprints and retractions Journals usually certify research through peer review before publishing it. Some studies are posted publicly earlier as preprints, before peer review, and some published papers are later retracted. Knowing these states protects you from relying on findings that are not yet certified or have been withdrawn.Editorially complete
Reading a study or a headline
- Correlation and causation Two things appearing together does not mean one caused the other. Many health headlines come from observational studies that find a “link” between a habit and a health outcome, but people with that habit may differ from others in many other ways that explain the result.Editorially complete
- How to read risk numbers A phrase like “cuts the risk in half” can mean a large or a very small difference, depending on the starting risk. Knowing the difference between absolute and relative risk is one of the most useful skills for understanding health news.Editorially complete
- Evaluating health news and websites Media and the internet are major sources of health information. Much of it is reliable, but some stories miss important details or are confusing or misleading. A few simple questions about the source and the underlying study help you tell the difference.Editorially complete
Research tools
- Study reader Enter the DOI of any published study to see its title, journal and year, its type according to the U.S. National Library of Medicine’s publication types (such as randomized trial or systematic review), its approximate place in the evidence pyramid, and whether it has been retracted, corrected or flagged with an expression of concern.Editorially complete
- Find recruiting clinical trials Search the ClinicalTrials.gov registry for studies that are recruiting now or soon, by condition name, optionally filtered by country. Results show each study’s title, phase, status, type and countries, with a link to its official record.Editorially complete
This section explains research methods and how to read evidence; it is not medical advice. The study reader and the trials search contact public research services only after you press search, and each explains what is sent before use.