The evidence provided from a Systematic Review can be 'upgraded' or 'downgraded' depending on the imprecision in the numerical estimates, the heterogeneity of the study-specific findings, the indirectness of the evidence, the risk of bias in the included studies and the potential impact of selective reporting and publication bias 23. A systematic, large-scale evaluation of the quality of the evidence provided by Systematic Reviews in the field of Anesthesiology would be of great interest. 2. Haynes B. Conducting systematic reviews. En: Haynes RB, Sackett DL, Guyatt GH, et al. Clinical epidemiology: how to do clinical practice research. 3edition. Philadelphia: Lippincott Williams & Wilkins; 2006. Chapter 2. 5. Jüni P, Witschi A, Bloch R, et al. The hazards of scoring the quality of clinical trials for meta-analysis. JAMA. 1999;282:1054-60. 6. Jüni P, Altman DG, Egger M. Systematic reviews in health care: assessing the quality of controlled clinical trials. BMJ. 2001;323:42-6. 7. Hróbjartsson A, Forfang E, Haahr MT, et al. Blinded trials taken to the test: an analysis of randomized clinical trials that report tests for the success of blinding. Int J Epidemiol. 2007;36:654-63. 8. Higgins JPT, Green S Ed. Cochrane handbook for systematic reviews of interventions version 5.1.0. Marzo 2011. [internet] [Consultado: marzo 2011]. Disponible en: www.cochrane-handbook.org. 9. Bero L, Oostvogel F, Bacchetti P, et al. Factors associated with findings of published trials of drug-drug comparisons: why some statins appear more efficacious than others. PLoS Med. 2007;4:e184. 10. Lexchin J, Bero LA, Djulbegovic B, et al. Pharmaceutical industry sponsorship and research outcome and quality: systematic review. BMJ. 2003;326:1167-70. 11. Van Luijn JC, van Loenen AC, Gribnau FW, et al. Choice of comparator in active control trials of new drugs. Ann Pharmacother. 2008;42:1605-12.
La evidencia suministrada a partir de una revisión sistemática puede "elevarse de nivel" o "bajarse de nivel" dependiendo de la imprecisión de los estimados numéricos, de la heterogeneidad de los hallazgos específicos del estudio, del carácter indirecto de la evidencia, del riesgo de sesgo en los estudios incluidos y del impacto potencial de reportes selectivos y sesgos en la publicación 23.