Classification	Description
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.