Preisser John S, Reboussin Beth A, Song Eun-Young, Wolfson Mark
Department of Biostatistics, University of North Carolina School of Public Health, Chapel Hill, North Carolina 27599-7420, USA.
Epidemiology. 2007 Sep;18(5):552-60. doi: 10.1097/ede.0b013e3181200199.
There is increasing recognition of the critical role of intracluster correlations of health behavior outcomes in cluster intervention trials. This study examines the estimation, reporting, and use of intracluster correlations in planning cluster trials. We use an estimating equations approach to estimate the intracluster correlations corresponding to the multiple-time-point nested cross-sectional design. Sample size formulae incorporating 2 types of intracluster correlations are examined for the purpose of planning future trials. The traditional intracluster correlation is the correlation among individuals within the same community at a specific time point. A second type is the correlation among individuals within the same community at different time points. For a "time x condition" analysis of a pretest-posttest nested cross-sectional trial design, we show that statistical power considerations based upon a posttest-only design generally are not an adequate substitute for sample size calculations that incorporate both types of intracluster correlations. Estimation, reporting, and use of intracluster correlations are illustrated for several dichotomous measures related to underage drinking collected as part of a large nonrandomized trial to enforce underage drinking laws in the United States from 1998 to 2004.
在整群干预试验中，健康行为结果的群内相关性的关键作用日益受到认可。本研究考察了在规划整群试验时群内相关性的估计、报告及应用。我们采用估计方程法来估计与多时间点嵌套横断面设计相对应的群内相关性。为规划未来试验，对纳入两种群内相关性的样本量公式进行了考察。传统的群内相关性是指在特定时间点同一社区内个体之间的相关性。第二种类型是同一社区内不同时间点个体之间的相关性。对于前后测嵌套横断面试验设计的“时间×条件”分析，我们表明，基于仅后测设计的统计效能考量通常不足以替代纳入两种群内相关性的样本量计算。作为1998年至2004年在美国实施未成年饮酒法律的一项大型非随机试验的一部分，针对与未成年饮酒相关的几种二分测量指标，阐述了群内相关性的估计、报告及应用。
