Levels of evidence
| Level of evidence A | Data derived from multiple randomised clinical trials# or meta-analyses. |
| Level of evidence B | Data derived from a single randomised clinical trial# or large nonrandomised studies. |
| Level of evidence C | Consensus of opinion of the experts and/or small studies, retrospective studies, registries. |
#: or large accuracy or outcome trial(s) in the case of diagnostic tests or strategies.