Sackett's evidence hierarchy

Sackett's evidence hierarchy ranks research studies based on how reliably they show whether a treatment works. At the top are well-designed, large clinical trials called systematic reviews and randomized controlled trials, which provide strongest evidence. Below are observational studies, case reports, and expert opinions, which are more prone to bias. The hierarchy helps clinicians evaluate the quality of evidence to make better healthcare decisions, with higher-level studies offering more confidence in their conclusions.