|Ia||Evidence obtained from meta-analysis or systematic review of randomized controlled trials.|
|Ib||Evidence obtained from at least one randomized controlled trial.|
|IIa||Evidence obtained from at least one well-designed controlled study without randomization.|
Evidence obtained from at least one other type of well-designed quasi-experimental study without randomization.
Evidence obtained from well-designed non-experimental descriptive studies, such as comparative studies, correlation studies and case studies.
Evidence obtained from expert committee reports or opinions and/or clinical experiences of respected authorities.