1. National Institute for Health and Clinical Excellence (NICE). [ http://www.nice.org.uk/ ]
2. Agency for Healthcare Research and Quality (AHRQ). [ http://www.ahrq.gov/ ]
3. The Norwegian Knowledge Centre for the Health Services (NOKC). [ http://www.kunnskapssenteret.no/Home ]
4. Oxman AD, Fretheim A, Schunemann HJ: Improving the use of research evidence in guideline development: introduction. Health Res Policy Syst. 2006, 4: 12-10.1186/1478-4505-4-12.
5. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) Working Group. [ http://www.gradeworkinggroup.org ]