Level of evidence |
I | Evidence demonstrated by means of meta-analyses of well-designed controlled trials or large randomized trials with clear-cut results (low rate of false-positive and false-negative errors, high power) |
II | Evidence demonstrated by means of small randomized trials with uncertain results (high rate of false-positive and false-negative errors, low power) |
III | Evidence demonstrated by means of nonrandomized concurrent cohort comparisons with contemporaneous controls |
IV | Evidence demonstrated by means of nonrandomized historical cohort comparisons |
V | Evidence demonstrated by means of case series without controls |
Grade of recommendation |
A | Supported by Level I evidence or multiple Level II, III or IV trials presenting concordant observations |
B | Supported by Level II, III or IV trials presenting generally concordant observations |
C | Supported by Level II, III or IV trials presenting nonconcordant observations |
D | Supported by few trials or no empiric evidence |