Contamination in trials: is cluster randomisation the answer?
Contamination in trials: is cluster randomisation the answer?
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DOI：
10.1136/bmj.322.7282.355
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发表时间：
2001-02-10
影响因子：
105.7
通讯作者：
Torgerson, DJ
中科院分区：
文献类型：
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作者：
Torgerson, DJ
大多数随机试验将个体参与者分配到不同的治疗中。然而，将受试者分组接受不同治疗的群集随机试验越来越受欢迎。1通常主张采用整群随机化，以最大限度地减少干预和对照受试者之间的治疗“污染”。例如，在一项饮食改变的试验中，对照组的人可能会了解实验饮食并自己采用它。它降低了干预措施有效性的点估计值，这种明显的降低可能导致II型错误，即由于观察到的效应量既没有统计学意义也没有临床意义而将有效的干预措施视为无效。虽然污染的威胁在一些对照试验中是一个问题，但在许多试验中可能没有太大的实际重要性。如果可能的话，试验者应该使用个体随机化，因为集群分配的缺点。聚类试验与招募偏倚问题有关，并且需要比类似的个体随机试验所需的更大的样本。在招募偏倚中，不同类型的受试者被选入试验的各个组，从而破坏了随机化的目的，而更大的样本量可能会增加试验的成本、长度或复杂性。本文介绍了集群试验的困难，并认为，污染的问题往往可以处理的个人随机化。
Most randomised trials allocate individual participants to different treatments. However, cluster randomised trials in which groups of subjects are allocated to different treatments are becoming increasingly popular. 1 Cluster randomisation is often advocated to minimise treatment “contamination” between intervention and control participants. For example, in a trial of dietary change, people in the control group might learn about the experimental diet and adopt it themselves.Contamination of control participants has two related effects. It reduces the point estimate of an intervention’s effectiveness and this apparent reduction may lead to a type II error—that is, rejection of an effective intervention as ineffective because the observed effect size was neither statistically nor clinically significant. Although the threat of contamination is an issue in some controlled trials, it may be not be of much practical importance in many. Trialists should use individual randomisation if possible because of the drawbacks of cluster allocation. Cluster trials are associated with problems of recruitment bias and the need for larger samples than would be required in similar, individually randomised trials. In recruitment bias, different sorts of participants are selected into the various arms of the trial, thereby defeating the objective of randomisation, while a larger sample size may increase the cost of a trial, its length, or its complexity. This paper describes the difficulties of cluster trials and argues that the problem of contamination can often be dealt with by individual randomisation.