Meerpohl Joerg J, Langer Gero, Perleth Matthias, Gartlehner Gerald, Kaminski-Hartenthaler Angela, Schünemann Holger
Deutsches Cochrane Zentrum, Institut für Medizinische Biometrie und Medizinische Informatik, Universitätsklinikum FreiburgundKlinik IV.
Z Evid Fortbild Qual Gesundhwes. 2012;106(6):457-69. doi: 10.1016/j.zefq.2012.06.014. Epub 2012 Jul 6.
In the GRADE approach, randomised trials start as high-quality evidence and observational studies as low-quality evidence, but both can be rated down if most of the relevant evidence comes from studies that suffer from a high risk of bias. Well-established limitations of randomised trials include failure to conceal allocation, failure to blind, loss to follow-up, and failure to appropriately consider the intention-to-treat principle. More recently, recognised limitations include stopping early for apparent benefit and selective reporting of outcomes according to the results. Key limitations of observational studies include use of inappropriate controls and failure to adequately adjust for prognostic imbalance. Risk of bias may vary across outcomes (e.g., loss to follow-up may be far less for all-cause mortality than for quality of life), a consideration that many systematic reviews ignore. In deciding whether to rate down for risk of bias - whether for randomised trials or observational studies-authors should not take an approach that averages across studies. Rather, for any individual outcome, when there are some studies with a high risk, and some with a low risk of bias, they should consider including only the studies with a lower risk of bias.
在GRADE方法中，随机对照试验一开始被视为高质量证据，观察性研究则被视为低质量证据，但如果大多数相关证据来自存在高偏倚风险的研究，那么这两种研究的证据等级都可能被下调。随机对照试验公认的局限性包括分配方案未隐匿、未设盲、失访以及未恰当考虑意向性分析原则。最近，公认的局限性还包括因表面上的益处而提前终止试验以及根据结果选择性报告结局。观察性研究的主要局限性包括使用了不恰当的对照以及未能充分校正预后不平衡。偏倚风险可能因结局而异（例如，全因死亡率的失访情况可能远低于生活质量的失访情况），许多系统评价都忽略了这一点。在决定是否因偏倚风险而降低证据等级时——无论是针对随机对照试验还是观察性研究——作者都不应采用对各项研究进行平均的方法。相反，对于任何单个结局，当存在一些高偏倚风险的研究和一些低偏倚风险的研究时，他们应考虑只纳入那些低偏倚风险的研究。
