Table 1: The Hierarchy of the Level Evidence in Descending Order of the Various Study Designs

Study Design Level of Evidence
Meta-analyses (MAs)
Systematic reviews (SRs)
Randomized controlled clinical trials (RCTs)
Non-randomized controlled clinical trials (Non-RCTs)
Cohort studies
Case-control studies
Crossover studies
Cross-sectional studies
Case studies
Consensus opinion of experts
Anecdotal reports or testimonies