| Class of evidence |
| Class 1 | Conditions for which there is evidence or general agreement that a given diagnostic evaluation procedure or treatment is beneficial, useful and effective. |
| Class 2 | Conditions for which there is conflicting evidence or a divergence of opinion about the usefulness or efficacy of a diagnostic evaluation, procedure or treatment. |
| Class 2a | Weight of evidence or opinion is in favour of usefulness or efficacy. |
| Class 2b | Usefulness or efficacy is less well established by evidence or opinion. |
| Class 3 | Conditions for which there is evidence or general agreement that a diagnostic evaluation, procedure or treatment is not useful or effective and in some cases may be harmful. |
| Grade of evidence |
| Level A | Data derived from multiple randomized clinical trials or meta-analyses. |
| Level B | Data derived from a single randomized trial, or nonrandomized studies. |
| Level C | Only consensus opinions of experts, case studies, or standard of care. |