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. Author manuscript; available in PMC: 2022 Aug 5.
Published in final edited form as: Urology. 2020 Jul 13;150:139–145. doi: 10.1016/j.urology.2020.06.056

Table 1:

Oxford Centre for Evidence-based Medicine – Levels of Evidence9

1a Systematic review (with a homogeneity of RCTs)
1b Individual RCT with narrow confidence interval
2a Systematic review (with homogeneity of cohort studies)
2b Individual cohort study (including low quality RCT)
2c Outcomes research; Ecological studies
3a Systematic Review (with homogeneity of case-control studies)
3b Individual case-control study
4 Case-series (and poor-quality cohort and case-control studies)
5 Expert opinion without explicit critical appraisal, or based on physiology, bench research, or “first principles”