OBJECTIVES To study the impact of blinding on estimated treatment effects, and their variation between trials; differentiating between blinding of patients, healthcare providers, and observers; detection bias and performance bias; and types of outcome (the MetaBLIND study). DESIGN Meta-epidemiological study. DATA SOURCE Cochrane Database of Systematic Reviews (2013-14). ELIGIBILITY CRITERIA FOR SELECTING STUDIES Meta-analyses with both blinded and non-blinded trials on any topic. REVIEW METHODS Blinding status was retrieved from trial publications and authors, and results retrieved automatically from the Cochrane Database of Systematic Reviews. Bayesian hierarchical models estimated the average ratio of odds ratios (ROR), and estimated the increases in heterogeneity between trials, for non-blinded trials (or of unclear status) versus blinded trials. Secondary analyses adjusted for adequacy of concealment of allocation, attrition, and trial size, and explored the association between outcome subjectivity (high, moderate, low) and average bias. An ROR lower than 1 indicated exaggerated effect estimates in trials without blinding. RESULTS The study included 142 meta-analyses (1153 trials). The ROR for lack of blinding of patients was 0.91 (95% credible interval 0.61 to 1.34) in 18 meta-analyses with patient reported outcomes, and 0.98 (0.69 to 1.39) in 14 meta-analyses with outcomes reported by blinded observers. The ROR for lack of blinding of healthcare providers was 1.01 (0.84 to 1.19) in 29 meta-analyses with healthcare provider decision outcomes (eg, readmissions), and 0.97 (0.64 to 1.45) in 13 meta-analyses with outcomes reported by blinded patients or observers. The ROR for lack of blinding of observers was 1.01 (0.86 to 1.18) in 46 meta-analyses with subjective observer reported outcomes, with no clear impact of degree of subjectivity. Information was insufficient to determine whether lack of blinding was associated with increased heterogeneity between trials. The ROR for trials not reported as double blind versus those that were double blind was 1.02 (0.90 to 1.13) in 74 meta-analyses. CONCLUSION No evidence was found for an average difference in estimated treatment effect between trials with and without blinded patients, healthcare providers, or outcome assessors. These results could reflect that blinding is less important than often believed or meta-epidemiological study limitations, such as residual confounding or imprecision. At this stage, replication of this study is suggested and blinding should remain a methodological safeguard in trials.

中文翻译：

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随机临床试验中盲法对估计治疗效果的影响：元流行病学研究。

目的研究盲法对估计治疗效果的影响及其在试验之间的差异；区分患者，医疗保健提供者和观察者的盲目性；检测偏差和性能偏差；和结果类型（MetaBLIND研究）。设计元流行病学研究。数据来源Cochrane系统评价数据库（2013-14）。选择研究的资格标准涉及任何主题的盲法和非盲法试验的荟萃分析。审查方法从试验出版物和作者中检索盲态，并从Cochrane系统评价数据库中自动检索结果。贝叶斯层次模型估算平均比值比（ROR），并估算试验之间异质性的增加，非盲试验（或状态不明）与盲试验的比较。二级分析针对隐藏分配，减员和试验规模的适当性进行了调整，并探讨了结果主观性（高，中，低）与平均偏倚之间的关联。ROR低于1表示在不致盲的试验中夸大了疗效估计。结果该研究包括142项荟萃分析（1153项试验）。在18项患者报告结果的荟萃分析中，患者不致盲的ROR为0.91（95％可信区间0.61至1.34），在14项对盲患者观察结果进行荟萃分析中，ROR为0.98（0.69至1.39）。29项具有医疗服务提供者决策结果（例如再入院）的荟萃分析中，医疗服务提供者不盲目的ROR为1.01（0.84至1.19），而0.97（0.64至1）则为0.91。45）在13项荟萃分析中，结果由盲人患者或观察者报告。在46项荟萃分析中，观察者缺乏视力的ROR为1.01（0.86至1.18），主观观察者报告了结果，但主观程度没有明显影响。尚不足以确定缺乏盲法是否与试验之间异质性增加有关。在74项荟萃分析中，未报告为双盲试验与双盲试验的ROR为1.02（0.90至1.13）。结论没有证据表明在有和没有盲人患者，医疗服务提供者或结果评估者的试验之间，估计治疗效果的平均差异。这些结果可能表明，盲目性不如通常认为的或亚流行病学研究的局限性重要，例如残留的混杂或不精确。在这个阶段，建议重复这项研究，盲法仍应是试验中的方法学保障。