| 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 |
[2] Combined oral contraceptive (dysmenorrhea caused by endometriosis): Wong CL, Farquhar C, Roberts H, Proctor M. Oral contraceptive pill for primary dysmenorrhoea. Cochrane Database Syst Rev. 2009 Oct 7;(4):CD002120. http://www.ncbi.nlm.nih.gov/pubmed/19821293
Combined oral contraceptive (dysmenorrhea caused by endometriosis): American College of Obstetricians and Gynecologists. ACOG practice bulletin no. 110: noncontraceptive uses of hormonal contraceptives. Obstet Gynecol. 2010;115(1):206-218.http://www.ncbi.nlm.nih.gov/pubmed/20027071
Combined oral (dysmenorrhea caused by endometriosis): Davis L, Kennedy SS, Moore J, Prentice A. Modern combined oral contraceptives for pain associated with endometriosis. Cochrane Database Syst Rev. 2007 Jul 18;(3):CD001019. http://www.ncbi.nlm.nih.gov/pubmed/17636650