Hierarchy of evidence

The hierarchy of evidence ranks different types of research based on their reliability for informing medical decisions. At the top are systematic reviews and meta-analyses, which combine results from many high-quality studies for the most comprehensive view. Below are well-designed randomized controlled trials, providing strong evidence about cause and effect. Observational studies, like cohort or case-control research, offer useful insights but are more prone to bias. Expert opinions and case reports sit lower in the hierarchy, as they are less systematic and more prone to individual bias. This hierarchy helps clinicians prioritize the most trustworthy evidence when making healthcare decisions.