Objective Monte Carlo simulation was used to study the influence of sample size and intra-class correlation on the inference of the intervention effect for a clustered randomized intervention stud-y. Methods The WaJd chi-square test and two different t tests in SAS PROC MIXED were evaluated in terms of their( 1) type 1 error(2) coverage. Results With more than 20 clusters per group,the Wald chi-square test had nominal type I error and coverage. The cluster degrees freedom method is better than the other two methods,but with more than 25 clusters per group,the performances of the three tests became similar. Conclusion The number of clusters per group is the key factor when inferring about the intervention effect, and caution is needed when choosing the right degrees of freedom for the t test in PROC MIXED.%目的 以Monte Carlo模拟评估样本量和群内相关系数对整群干预试验中干预效应推断的影响.方法 干预效应的推断通过SAS PROC MIXED的Wald卡方检验和两种不同自由度的t检验,评价第一类错误和可信区间覆盖率.结果 设计整群干预试验时,干预组和对照组群数应大于20,可提高干预效应卡方检验的可信区间覆盖率并减少一类错误.群自由度法优于其他两种方法,但当每组群数大于25时,MIXED中不同检验结果接近.结论群数是影响干预效应推断的最重要因素,而MIXED过程的t检验要选择恰当的自由度.
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