Abstract

The concepts and implementation of standardized mean differences and minimum effect tests have been emphasized in ANOVA. The corresponding processes and implications are, however, not yet well explicated in the context of ANCOVA. To enhance the usefulness of ANCOVA, this article describes the minimum effect tests of standardized contrast as a valuable alternative to the hypothesis testing of no effect difference and the conventional evaluation of unstandardized effects in ANCOVA. Power and sample size procedures are developed to accommodate covariate randomness and imbalance for randomized and nonrandomized designs. The data from a clinical study of comparing two treatments for gingivitis are used to illustrate the application of the suggested approaches. The emphases of numerical appraisal are on the merit of minimum effect detection in comparative analysis and the influence of covariate feature in power and sample size computation. The proposed power and sample size calculations improve upon approximate formulas by fully accounting for the stochastic property and intrinsic disparity of the covariate variables. Computer algorithms are available for calculating the p-value, power level, and sample size of one- and two-sided minimum effect tests.

摘要

方差分析中强调了标准化平均差异和最小效应检验的概念和实施。然而，在 ANCOVA 的背景下，相应的过程和影响尚未得到很好的解释。为了提高 ANCOVA 的实用性，本文将标准化对比度的最小效应检验作为无效应差异的假设检验和 ANCOVA 中非标准化效应的常规评估的一种有价值的替代方法。制定功效和样本量程序以适应随机和非随机设计的协变量随机性和不平衡性。比较两种牙龈炎治疗的临床研究数据用于说明建议方法的应用。数值评价的重点是比较分析中最小效应检测的优点以及协变量特征在功效和样本量计算中的影响。通过充分考虑协变量变量的随机属性和内在差异，建议的功效和样本量计算改进了近似公式。计算机算法可用于计算一侧和两侧最小效应检验的p值、功效水平和样本量。