Table 2.

Levels of evidence used in grading the articles (modified from the 2009 Oxford Centre for Evidence-based Medicine Levels of Evidence and the International Consultation on Urological Diseases)^{7, 8}

Level	Study Design or Type
1a	Systematic review of RCTs
1b	Individual RCT (good quality)
2a	Systematic review of cohort studies
2b	Individual cohort study, low quality RCT
3a	Systematic review of case control studies
3b	Individual case control study
4a	Good quality case-series, poor quality cohort or case control study
4b	Cross-sectional study
5	Expert opinion

RCT Randomized controlled trial