Lemme Francesca, van Breukelen Gerard J P, Berger Martijn P F
Department of Methodology and Statistics, Maastricht University, Maastricht, The Netherlands.
Stat Med. 2016 Oct 30;35(24):4320-4334. doi: 10.1002/sim.7003. Epub 2016 Jun 7.
Typically, clusters and individuals in cluster randomized trials are allocated across treatment conditions in a balanced fashion. This is optimal under homogeneous costs and outcome variances. However, both the costs and the variances may be heterogeneous. Then, an unbalanced allocation is more efficient but impractical as the outcome variance is unknown in the design stage of a study. A practical alternative to the balanced design could be a design optimal for known and possibly heterogeneous costs and homogeneous variances. However, when costs and variances are heterogeneous, both designs suffer from loss of efficiency, compared with the optimal design. Focusing on cluster randomized trials with a 2 × 2 design, the relative efficiency of the balanced design and of the design optimal for heterogeneous costs and homogeneous variances is evaluated, relative to the optimal design. We consider two heterogeneous scenarios (two treatment arms with small, and two with large, costs or variances, or one small, two intermediate, and one large costs or variances) at each design level (cluster, individual, and both). Within these scenarios, we compute the relative efficiency of the two designs as a function of the extents of heterogeneity of the costs and variances, and the congruence (the cheapest treatment has the smallest variance) and incongruence (the cheapest treatment has the largest variance) between costs and variances. We find that the design optimal for heterogeneous costs and homogeneous variances is generally more efficient than the balanced design and we illustrate this theory on a trial that examines methods to reduce radiological referrals from general practices. Copyright © 2016 John Wiley & Sons, Ltd.
通常，整群随机试验中的群组和个体是以均衡的方式分配到不同治疗条件下的。在成本和结果方差均一的情况下，这是最优的分配方式。然而，成本和方差可能都是异质的。那么，不均衡分配会更有效率，但由于在研究设计阶段结果方差未知，所以这种方法不切实际。对于均衡设计而言，一种可行的替代方案可能是针对已知的、可能异质的成本和均一的方差设计出的最优方案。然而，当成本和方差都是异质的时候，与最优设计相比，这两种设计都会出现效率损失。针对具有2×2设计的整群随机试验，相对于最优设计，评估了均衡设计以及针对异质成本和均一方差的最优设计的相对效率。我们在每个设计层面（群组、个体以及两者皆有）考虑了两种异质情况（两个治疗组成本或方差较小，另外两个治疗组成本或方差较大，或者一个治疗组成本或方差较小，两个治疗组成本或方差中等，一个治疗组成本或方差较大）。在这些情况下，我们计算了这两种设计的相对效率，它是成本和方差的异质程度以及成本与方差之间的一致性（最便宜的治疗方法方差最小）和不一致性（最便宜的治疗方法方差最大）的函数。我们发现，针对异质成本和均一方差的最优设计通常比均衡设计更有效率，并且我们在一项检验减少全科医疗中放射学转诊方法的试验中阐述了这一理论。版权所有© 2016约翰·威利父子有限公司。
