Sample size estimation for longitudinal designs with attrition: Comparing time-related contrasts between two groups
Sample size estimation for longitudinal designs with attrition: Comparing time-related contrasts between two groups
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DOI：
10.3102/10769986024001070
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发表时间：
1999-03-01
影响因子：
2.4
通讯作者：
Waternaux, C
中科院分区：
文献类型：
--
作者：
Hedeker, D;Gibbons, RD;Waternaux, C
估计样本量的公式，提供了特定水平的权力，从纵向设计的显着性测试，允许受试者的磨损。推导这些公式是为了比较两组在研究时间点之间群体平均值的单自由度对比。这种类型的对比通常可以捕获两组重复测量设计中的主效应和交互效应。例如，跨时间的平均值或跨时间的特定趋势的两组比较（例如，线性的或二次的）。由于具有损耗的纵向数据通常使用不平衡的重复测量模型（重复测量具有结构化的方差-协方差矩阵）或不完整纵向数据的随机效应模型进行分析，因此允许重复测量的方差-协方差矩阵采用各种形式。表格列出了假设复合对称、一阶自回归结构和非平稳随机效应结构的样本量确定。提供的例子来说明使用的公式，和一个计算机程序实现的过程是从第一作者。
Formulas for estimating sample sizes are presented to provide specified levels of power for tests of significance from a longitudinal design allowing for subject attrition. These formulas are derived for a comparison of two groups in terms of single degree-of-freedom contrasts of population means across the study timepoints. Contrasts of this type can often capture the main and interaction effects in a two-group repeated measures design. For example, a two-group comparison of either an average across time or a specific trend across time (e.g., linear or quadratic) can be considered. Since longitudinal data with attrition are often analyzed using an unbalanced repeated measures model (with a structured variance-covariance matrix for the repeated measures) or a random-effects model for incomplete longitudinal data, the variance-covariance matrix of the repeated measures is allowed to assume a variety of forms. Tables are presented listing sample size determinations assuming compound symmetry, a first-order autoregressive structure, and a non-stationary random-effects structure. Examples are provided to illustrate use of the formulas, and a computer program implementing the procedure is available from the first author.