3. Hierarchy of Evidence
1 a Evidence obtained from Meta analysis of RCTs.
1 b Evidence obtained from at least one individual RCT.
1 c Evidence obtained from all on none case-series.
2 a Evidence obtained from Systematic Review of Cohort studies.
2 b Evidence obtained from a single cohort or a poor RCT.
2 c Outcomes research ecological studies.
3 a Systematic Review of Case controlled studies.
3 b Individual case controlled study.
4 Case series. ( including poor quality cohorts and case controls)
5 Evidence obtained from expert committee reports or opinions and /
or clinical experiences of respected authorities without explicit
critical appraisal.