Table 5.
Level of evidence and grades of recommendation (adapted from the Infectious Diseases Society of America—United States Public Health Service Grading System)a
| Level of evidence | |
|---|---|
| I | Evidence from at least one large randomized, controlled trial of good methodological quality (low potential for bias) or meta-analysis of well-conducted randomised trials without heterogeneity |
| II | Small randomized trials or large randomized trials with a suspicion of bias (lower methodological quality) or meta-analysis of such trials or of trials with demonstrated heterogeneity |
| III | Prospective cohort studies |
| IV | Retrospective cohort studies or case-control studies |
| V | Studies without control group, case reports, expert opinions |
| Grades of recommendation | |
| A | Strong evidence for efficacy with a substantial clinical benefit, strongly recommended |
| B | Strong or moderate evidence for efficacy but with a limited clinical benefit, generally recommended |
| C | Insufficient evidence for efficacy or benefit does not outweigh the risk or the disadvantages (adverse events, costs, …), optional |
| D | Moderate evidence against efficacy or for adverse outcome, generally not recommended |
| E | Strong evidence against efficacy or for adverse outcome, never recommended |
a
Senkus E, Kyriakides S, Ohno S, Penault-Llorca F, Poortmans P, Rutgers E et al. Primary breast cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Annals of Oncology. 2015; 26(suppl 5):v8–v30. (Permission for reproduction granted by Annals of Oncology).