Level | Type of evidence |
1A | Systematic review (with homogeneity) of RCTs |
1B | Individual RCT (with narrow confidence intervals) |
1C | All or none study |
2A | Systematic review (with homogeneity) of cohort studies |
2B | Individual cohort study (including low quality RCT, e.g., <80% follow-up) |
2C | “Outcomes” research; Ecological studies |
3A | Systematic review (with homogeneity) of case-control studies |
3B | Individual case-control study |
4 | Case series (and poor quality cohort and case-control study |
5 | Expert opinion without explicit critical appraisal or based on physiology bench research or “first principles” |