Table 1

Summary of ‘The Oxford Levels of Evidence 2’ (Adapted from the 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
  • OCEBM, Oxford Centre for Evidence-Based Medicine.