Among study designs, which has the greatest quality of evidence?

• A. Randomized controlled trial
• B. Cohort study
• C. Case series
• D. Meta-analysis

Answer: (D)

Meta-analysis represents the strongest level of evidence because it combines results from multiple studies using a systematic approach. By pooling data, it increases the overall sample size, improves precision of the estimated effect, and allows assessment of consistency across different populations and settings. This synthesis reduces random error that can affect a single study and can reveal true effects that individual trials might miss. When performed well as part of a systematic review with transparent methods for searching, selecting studies, and evaluating bias, meta-analysis typically provides higher-quality evidence than any single randomized trial, cohort study, or case series. Of course, its strength depends on the quality of the included studies and the rigor of the methods used.