Categories of evidence
| Category | Evidence from: |
|---|---|
| 1A | Meta-analysis of randomised controlled trials |
| 1B | At least one randomised controlled trial |
| 2A | At least one controlled study without randomisation |
| 2B | At least one type of quasi-experimental study |
| 3 | Descriptive studies, such as comparative studies, correlation studies, or case-control studies |
| 4 | Expert committee reports or opinions and/or clinical experience of respected authorities |