Which study design provides the highest level of evidence?

The evidence hierarchy from highest to lowest is: (1) Systematic review with meta-analysis; (2) Randomized controlled trials (RCTs); (3) Cohort studies; (4) Case-control studies; (5) Cross-sectional studies; (6) Case reports/series; (7) Expert opinion. A systematic review with meta-analysis sits at the top because it systematically identifies, critically appraises, and statistically synthesizes all available high-quality evidence on a topic, providing the most reliable estimate of treatment effects with the greatest precision. In clinical dentistry, Cochrane Reviews represent the gold standard of this evidence type.