Department of Biostatistical Sciences, Division of Public Health Sciences, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157-1063, USA.
Stat Med. 2010 May 10;29(10):1137-44. doi: 10.1002/sim.3873.
In any study it is essential to select the sample size carefully to ensure adequate power. For many studies this is simple: recruit a desired number of subjects within each group, conduct measurements, and perform the statistical test. In some studies (e.g. observational studies), however, the group membership is unknown at recruitment. In this paper we examine the effect of random group sizes on power. Additionally, we consider the situation when the group proportions are unknown and specified by a prior distribution. The problem that initially motivated this research is presented (power for a 2-by-2 table), as are examples using continuous outcomes. We find that standard estimates of power using expected group sizes can over or underestimate power. SAS macros are available at http://www.phs.wfubmc.edu/public/wambrosi/RandomPower.
在任何研究中，精心选择样本量以确保足够的功效至关重要。对于许多研究来说，这很简单：在每个组中招募所需数量的受试者，进行测量，然后进行统计检验。然而，在某些研究（例如观察性研究）中，在招募时不知道组别的归属。在本文中，我们研究了随机组大小对功效的影响。此外，我们还考虑了当组比例未知且由先验分布指定的情况。最初推动这项研究的问题（2x2 表的功效）以及使用连续结果的示例都有介绍。我们发现，使用预期组大小的标准功效估计值可能会过高或过低估计功效。SAS 宏可在 http://www.phs.wfubmc.edu/public/wambrosi/RandomPower 获得。
