Table 1 Levels of evidence and grades of recommendation

I

Meta-analysis of multiple well-designed, controlled studies; randomized trials with low rates of false-positive and low false-negative errors (high power)

A

Evidence rated as level I or consistent findings from multiple studies at levels II, III, or IV

II

At least one well-designed experimental study; randomized trials with high rates of false-positive and high false-negative errors (low power)

B

Evidence at levels II, III or IV, and generally consistent findings

III

Well-designed, quasi-experimental studies such as non-randomized, controlled, single-group, preoperative and correlation descriptive studies, and case studies

C

Evidence at levels II, III or IV, but inconsistent findings

IV

Well-designed, non-experimental studies such as comparative and correlation descriptive studies, and case studies

D

Little or no systematic empirical evidence

V

Case reports and clinical examples