| Level I | Good quality evidence |
Systematic review of RCTs with consistent findings High quality individual RCT |
| Level II |
Limited quality patient orientated evidence |
Systematic review of lower quality studies or studies with inconsistent findings Low quality clinical trial Cohort studies Case-control studies |
| Level III | Other |
Consensus guidelines, extrapolations from bench research, usual practice, opinion, disease-oriented evidence (intermediate or physiologic outcomes only), or case series |
[31] Copper IUD – emergency contraception: Cheng L, Che Y, Gülmezoglu AM. Interventions for emergency contraception. Cochrane Database Syst Rev. 2012 Aug 15;8:CD001324. http://www.ncbi.nlm.nih.gov/pubmed/22895920