Power and sample-size calculations for trials that compare slopes over time: Introducing the slopepower command.
Power and sample-size calculations for trials that compare slopes over time: Introducing the slopepower command.
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比较坡度随时间变化的试验的功率和样本大小计算：介绍slopepower命令。
DOI：
10.1177/1536867x211045512
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
Mulick A
中科院分区：
文献类型：
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作者：
Nash S;Morgan KE;Frost C;Mulick A
旨在减缓疾病进展的干预试验可以使用线性混合模型，通过比较治疗组和未治疗组随时间的变化（斜率）来分析连续结果。为了进行这样一项试验的样本大小计算，必须对控制结果的受试者之间和受试者内部变异性的参数进行估计，这些参数通常是未知的。对于这样的试验设计，样本量计算所需的代数也可能很复杂。我们编写了一个新的用户友好命令，slopepower，它执行比较坡度结果的试验的样本大小或功率计算。该软件包基于线性混合模型方法，Frost， Kenward和Fox（2008年，医学统计27:3717-3731）对此设置进行了描述。在该方法的第一阶段，斜率功率从线性混合模型中获得平均斜率的估计值以及方差和协方差，这些模型拟合先前收集的用户提供的数据。在第二阶段，这些估计与用户关于治疗的目标有效性和未来试验设计的输入相结合，以给出样本量或统计能力的估计。在本文中，我们介绍了slopepower命令，简要解释了其背后的方法，并演示了如何使用它来帮助计划试验和比较不同试验设计所需的样本量。
Trials of interventions that aim to slow disease progression may analyze a continuous outcome by comparing its change over time—its slope—between the treated and the untreated group using a linear mixed model. To perform a sample-size calculation for such a trial, one must have estimates of the parameters that govern the between- and within-subject variability in the outcome, which are often unknown. The algebra needed for the sample-size calculation can also be complex for such trial designs. We have written a new user-friendly command, slopepower, that performs sample-size or power calculations for trials that compare slope outcomes. The package is based on linear mixed-model methodology, described for this setting by Frost, Kenward, and Fox (2008, Statistics in Medicine 27: 3717–3731). In the first stage of this approach, slopepower obtains estimates of mean slopes together with variances and covariances from a linear mixed model fit to previously collected user-supplied data. In the second stage, these estimates are combined with user input about the target effectiveness of the treatment and design of the future trial to give an estimate of either a sample size or a statistical power. In this article, we present the slopepower command, briefly explain the methodology behind it, and demonstrate how it can be used to help plan a trial and compare the sample sizes needed for different trial designs.