1. Agency for Health Care Policy and Research (AHCPR). Acute pain management: operative and medical procedures and trauma. Clinical practice guideline No.1. AHCPR Publication 1992 No. 92–0023, Appendix B. available at:
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?rid=hstat6.table.9286
2. Alderson P, Green S, Higgins J (2004) Cochrane Reviewers’ Handbook. Handbook 4.2.1. [updated December 2003]. John Wiley & Sons Ltd, Chichester
3. Altman DG, Bland JM (1995) Absence of evidence is not evidence of absence. BMJ 311 :485
4. Bornhöft G, Maxion-Bergemann S, Wolf U, Kienle G, Michalsen A, Vollmar H, Gilbertson S, Matthiessen P (2006) Checklist for the qualitative evaluation of clinical studies with particular focus on external validity and model validity. BMC Med Res Methodol 6:56
5. Bundesamt für Sozialversicherung der Schweiz (ed) (1996)Handbuch zur Standardisierung der medizinischen und wirtschaftlichen Bewertung medizinischer Leistungen, 3rd edn. Bern