Table 1

Summary of “The Oxford Levels of Evidence 2.” (adapted from OCEBM Levels of Evidence Working Group)

Level 1Level 2Level 3Level 4Level 5
Systematic review or meta-analysisRandomized trial or observational study with dramatic effectNon-randomized, controlled cohort, or follow-up studyCase series, case–control, or historically controlled studyMechanism-based reasoning