| Level |
Definition |
| A |
High-quality randomized controlled trial (RCT) |
| A |
High-quality meta-analysis (quantitative systematic review) |
| B |
Nonrandomized clinical trial |
| B |
Nonquantitative systematic review |
| B |
Lower quality RCT |
| B |
Clinical cohort study |
| B |
Case-control study |
| B |
Historical control |
| B |
Epidemiologic study |
| C |
Consensus |
| C |
Expert opinion |
| D |
Anecdotal evidence |
| D |
In vitro or animal study |
| D |
Theoretical based on pharmacology |
