The unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials
The unpredictability paradox: review of empirical comparisons of randomised and non-randomised clinical trials
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DOI：
10.1136/bmj.317.7167.1185
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发表时间：
1998-10-31
影响因子：
--
通讯作者：
Oxman, AD
中科院分区：
文献类型：
--
作者：
Kunz, R;Oxman, AD
目的总结随机临床试验与非随机临床试验、充分隐藏随机分配与不充分隐藏随机分配试验的比较，和高质量的试验与低质量的试验，其中随机化的效果不能与其他方法学策略的效果分开。对临床试验的分析，包括随机化和效果估计之间关系的经验评估数据来源：科克伦综述方法学数据库、Medline、SciSearch、参考文献、手工检索期刊、与方法学家的个人交流，主要结果测量随机化与效应估计之间的关系结果比较随机对照试验与非随机对照试验的11项研究（8次用于评价同一干预措施，3次用于评价不同的干预措施），两项研究比较了充分隐藏随机分配和不充分隐藏随机分配的试验，五项研究评估了质量评分和治疗效果估计之间的关系。未能使用随机分配和隐藏分配与估计效应的相对增加150%或更多，相对减少高达90%，估计效应的反转，在某些情况下，没有差异。平均而言，未能使用随机化或充分隐藏的分配导致更大的估计效果，由于在非随机选择的对照组与随机选择的对照组相比，预后较差。结论未能使用充分隐藏的随机分配可以扭曲的明显效果的护理在任何方向，导致效果似乎比他们真的更大或更小。这些失真的大小可以与要检测的效应的大小一样大或更大。
Objective To summarise comparisons of randomised clinical trials and non-randomised clinical trials, trials with adequately concealed random allocation versus inadequately concealed random allocation, and high quality trials versus low quality trials where the effect of randomisation could not be separated from the effects of other methodological manoeuvres.Design Systematic reviewSelection criteria Cohorts or meta-analyses of clinical trials that included an empirical assessment of the relation between randomisation and estimates of effectData sources Cochrane Review Methodology Database, Medline, SciSearch, bibliographies, hand searching of journals, personal communication with methodologists, and the reference lists of relevant articles.Main outcome measures Relation between randomisation and estimates of effectResults Eleven studies that compared randomised controlled trials with non-randomised controlled trials (eight for evaluations of the same intervention and three across different interventions), two studies that compared trials with adequately concealed random allocation and inadequately concealed random allocation, and five studies that assessed the relation between quality scores and estimates of treatment effects, were identified. Failure to use random allocation and concealment of allocation were associated with relative increases in estimates of effects of 150% or more, relative decreases of up to 90%, inversion of the estimated effect and, in some cases, no difference. On average, failure to use randomisation or adequate concealment of allocation resulted in larger estimates of effect due to a poorer prognosis in non-randomly selected control groups compared with randomly selected control groups.Conclusions Failure to use adequately concealed random allocation can distort the apparent effects of care in either direction, causing the effects to seem either larger or smaller than they really are. The size of these distortions can be as large as or larger than the size of the effects that are to be detected.