Borm George F, Houben Rein M G J, Welsing Paco M J, Zielhuis Gerhard A
Department of Epidemiology and Biostatistics, 133 EPIB, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500HB Nijmegen, The Netherlands.
J Clin Epidemiol. 2006 Jan;59(1):1-6. doi: 10.1016/j.jclinepi.2005.03.020. Epub 2005 Nov 2.
Many clinical studies have more than one objective, either formally or informally, but this is not usually taken into account in the determination of the sample size. We investigated the overall power of a study, that is, the probability that all the objectives will be met.
We calculated the overall power in the case that the study has two primary outcome variables and in the case that one outcome variable is evaluated on two subsets, in particular, the Per Protocol group and the Intention to Treat group.
A power of 80% for each of the two end points leads to poor power for the end points combined. However, a power of 90% preserves better the overall power. The power of the Per Protocol analysis can be higher or lower than the power of the Intention to Treat analysis.
Power should be calculated for all end points combined, and it should be at least 90% for each primary end point. If the sample size for the intention-to-treat analysis is determined by adding a percentage of "nonevaluable subjects" to the sample size required for the per protocol analysis, then this may lead to an underpowered study.
许多临床研究都有一个以上的目标，无论是正式的还是非正式的，但在确定样本量时通常不会考虑这一点。我们研究了一项研究的总体检验效能，即所有目标均能达成的概率。
我们计算了研究中有两个主要结局变量的情况以及一个结局变量在两个亚组（特别是符合方案组和意向性分析组）中进行评估的情况下的总体检验效能。
两个终点各自的检验效能为80%会导致合并终点的检验效能较低。然而，90%的检验效能能更好地保持总体检验效能。符合方案分析的检验效能可能高于或低于意向性分析的检验效能。
应计算所有合并终点的检验效能，且每个主要终点的检验效能应至少为90%。如果意向性分析的样本量是通过在符合方案分析所需样本量基础上增加一定比例的“无评估价值受试者”来确定，那么这可能会导致研究检验效能不足。
