Assessing standardized contrast effects in ANCOVA: Confidence intervals, precision evaluations, and sample size requirements

• Published in: PloS one 2023-02, Vol.18 (2), p.e0282161-e0282161
• Main Author: Shieh, Gwowen
• Format: Article
• Language: English
• Subjects: Analysis of covariance; Biology and Life Sciences; Computer and Information Sciences; Computer programs; Confidence Intervals; Data entry; Dispersion measures (Statistics); Evaluation; Models, Statistical; Normal distribution; Physical Sciences; Research and analysis methods; Research Design; Sample Size; Sample variance; Software; Statistical analysis; Units of measurement
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0282161

Standardized effect sizes and confidence intervals are useful statistical assessments for comparing results across different studies when measurement units are not directly comparable. This paper aims to describe and compare confidence interval estimation methods for the standardized contrasts of treatment effects in ANCOVA designs. Sample size procedures are also presented to assure that the resulting confidence intervals yield informative estimation with adequate precision. Exact interval estimation approach has theoretical and empirical advantages in coverage probability and interval width over the approximate interval procedures. Numerical investigations of the existing method reveal that the omission of covariate variables has a negative impact on sample size calculations for precise interval estimation, especially when there is disparity in influential covariate variables. The proposed approaches and developed computer programs fully utilize covariate properties in interval estimation and provide accurate sample size determinations under the precision considerations of the expected interval width and the assurance probability of interval width.