Ia - Evidence obtained from meta-analysis or systematic reviews of randomized controlled trialsG, and/or synthesis of multiple studies primarily of quantitative research.
Ib - Evidence obtained from at least one randomized controlled trial.
IIa - Evidence obtained from at least one well-designed controlled study without randomization.
IIb - Evidence obtained from at least one other type of well-designed quasi-experimental study, without randomization.
III - Synthesis of multiple studies primarily of qualitative research.
IV- Evidence obtained from well-designed non-experimental observational studies, such as analytical studies or descriptive studies, and/or qualitative studies.
V- Evidence obtained from expert opinion or committee reports, and/or clinical experiences of respected authorities.
Adapted from the Scottish Intercollegiate Guidelines Network (Scottish Intercollegiate Guidelines Network [SIGN], 2011) and Pati (2011).