Table 6.

Classification system for levels of evidence and grades of recommendation [28].

Type of evidence
Level I—meta-analysis of multiple, well-designed, controlled studies. Randomized studies with low type 1 and type 2 errors (high power) are also considered.
Level II—evidence obtained from at least one, well-designed experimental study. Randomised trials with high type 1 and/or type 2 errors (low power) are also considered.
Level III—well-designed, quasiexperimental studies such as nonrandomised, controlled single-group, prepost, cohort, time, or matched case-control series.
Level IV—well-designed, nonexperimental studies, such as comparative and correlational descriptive and case studies.
Level V—case reports and clinical examples.
Grade of recommendation
Grade A—evidence of level I or consistent findings from multiple levels II, III, and IV studies.
Grade B—evidence of levels II, III, or IV with generally consistent findings.
Grade C—evidence of levels II, III, or IV but findings are inconsistent.
Grade D—minimal or no systematic empirical evidence.