Department of Epidemiology, Biostatistics and HTA, 133, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
J Clin Epidemiol. 2012 Feb;65(2):132-7. doi: 10.1016/j.jclinepi.2011.05.006. Epub 2011 Aug 12.
Balance of prognostic factors between treatment groups is desirable because it improves the accuracy, precision, and credibility of the results. In cluster-controlled trials, imbalance can easily occur by chance when the number of cluster is small. If all clusters are known at the start of the study, the "best balance" allocation method (BB) can be used to obtain optimal balance. This method will be compared with other allocation methods.
We carried out a simulation study to compare the balance obtained with BB, minimization, unrestricted randomization, and matching for four to 20 clusters and one to five categorical prognostic factors at cluster level.
BB resulted in a better balance than randomization in 13-100% of the situations, in 0-61% for minimization, and in 0-88% for matching. The superior performance of BB increased as the number of clusters and/or the number of factors increased.
BB results in a better balance of prognostic factors than randomization, minimization, stratification, and matching in most situations. Furthermore, BB cannot result in a worse balance of prognostic factors than the other methods.
治疗组之间的预后因素平衡是理想的，因为它可以提高结果的准确性、精度和可信度。在聚类对照试验中，当聚类数量较小时，不平衡很容易偶然发生。如果在研究开始时就知道所有的聚类，那么可以使用“最佳平衡”分配方法（BB）来获得最佳平衡。本文将比较 BB 与其他分配方法的效果。
我们进行了一项模拟研究，比较了 BB、最小化、无限制随机化和匹配在 4 到 20 个聚类和 1 到 5 个聚类水平分类预后因素时的平衡效果。
在 13%到 100%的情况下，BB 比随机化产生了更好的平衡效果，在 0%到 61%的情况下比最小化好，在 0%到 88%的情况下比匹配好。BB 的优越性能随着聚类数量和/或因素数量的增加而增加。
在大多数情况下，BB 比随机化、最小化、分层和匹配在预后因素的平衡方面效果更好。此外，BB 不会导致预后因素的平衡比其他方法更差。
