| 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 |
[15] Letrozole, oral: National Department of Health: Affordable Medicines, EDP-Adult Hospital level. Medicine Review: Letrozole for infertility associated with anovulation, April 2020. http://www.health.gov.za/
Letrozole, oral: Franik S, Eltrop SM, Kremer JA, Kiesel L, Farquhar C. Aromatase inhibitors (letrozole) for subfertile women with polycystic ovary syndrome. Cochrane Database Syst Rev. 2018;5(5):CD010287. https://pubmed.ncbi.nlm.nih.gov/29797697/