| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[6] Aspirin, oral (stable angina): Antithrombotic Trialists' Collaboration. Collaborative meta-analysis of randomised trials of antiplatelet therapy for prevention of death, myocardial infarction, and stroke in high risk patients.BMJ. 2002 Jan 12;324(7329):71-86. Erratum in: BMJ 2002 Jan 19;324(7330):141. https://www.ncbi.nlm.nih.gov/pubmed/11786451