When evaluating the strength of evidence in clinical research, which study design is considered the highest level of evidence?

The hierarchy of evidence places randomized controlled trials (RCTs) at a high level because random allocation minimizes selection bias and confounding variables. Among individual study types, the RCT provides the strongest evidence for causality. Systematic reviews and meta-analyses of multiple RCTs are ranked even higher, but among the options given, the RCT is the best study design. Narrative literature reviews, case studies, and cross-sectional studies are lower on the evidence hierarchy.