Using the half normal distribution to quantify covariate balance in cluster-randomized pragmatic trials.
Using the half normal distribution to quantify covariate balance in cluster-randomized pragmatic trials.
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DOI：
10.1186/s13063-021-05122-x
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发表时间：
2021-03-06
期刊：
影响因子：
2.5
通讯作者：
Roth DL
中科院分区：
文献类型：
--
作者：
Huang J;Roth DL
务实试验通常由整群随机对照试验(C-RCT)组成，在这些试验中，现有诊所或站点的工作人员提供干预措施，在站点水平进行随机化。协变量约束随机化(CCR)方法通常被推荐用来最小化干预和控制组之间的重要部位特征的不平衡，因为当要随机化的单位数相对较小时，在简单的随机化中可能会偶然发生相当大的不平衡。CCR方法最初涉及多个随机分配，评估每次随机化在站点级别协变量上实现的平衡，以及最终选择产生可接受平衡的分配。然而，对于如何评估不平衡或确定有足够余额的拨款，没有明确的共识。在本文中，我们描述了一个总体不平衡指数(I)，该指数是基于标准化均值差对场地特征的绝对值的平均值。我们推导出I的理论分布，然后进行模拟研究，以检验其在变化的协变量分布和相互关系下的经验性质。I的期望值为0.798，假设站点特性独立，方差为0.363/k，其中k是平衡的站点特性数量。仿真结果表明，只要k大于3，且协变量之间的相关性不太强，I的性质在不同协变量情况下都是稳健的。我们建议，低于10%的i值表示CCR中有足够的总体站点余额。除了总体平衡标准外，可接受的随机化的定义还可能包括预先指定的个别协变量标准。
Pragmatic trials often consist of cluster-randomized controlled trials (C-RCTs), where staff of existing clinics or sites deliver interventions and randomization occurs at the site level. Covariate-constrained randomization (CCR) methods are often recommended to minimize imbalance on important site characteristics across intervention and control arms because sizable imbalances can occur by chance in simple randomizations when the number of units to be randomized is relatively small. CCR methods involve multiple random assignments initially, an assessment of balance achieved on site-level covariates from each randomization, and the final selection of an allocation that produces acceptable balance. However, no clear consensus exists on how to assess imbalance or identify allocations with sufficient balance. In this article, we describe an overall imbalance index (I) that is based on the mean of the absolute value of the standardized differences in means on the site characteristics. We derive the theoretical distribution of I, then conduct simulation studies to examine its empirical properties under the varying covariate distributions and inter-correlations. I has an expected value of 0.798 and, assuming independent site characteristics, a variance of 0.363/k, where k is the number of site characteristics being balanced. Simulations indicated that the properties of I are robust under varying covariate circumstances as long as k is greater than 3 and the covariates are not too highly inter-correlated. We recommend that values of I below the 10th percentile indicate sufficient overall site balance in CCRs. Definitions of acceptable randomizations might also include individual covariate criteria specified in advance, in addition to overall balance criteria.
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