title: Effects of correlation and missing data on sample size estimation in longitudinal clinical trials.
abstract: In longitudinal clinical trials, a common objective is to compare the rates of changes in an outcome variable between two treatment groups. Generalized estimating equation (GEE) has been widely used to examine if the rates of changes are significantly different between treatment groups due to its robustness to misspecification of the true correlation structure and randomly missing data. The sample size formula for repeated outcomes is based on the assumption of missing completely at random and a large sample approximation. A simulation study is conducted to investigate the performance of GEE sample size formula with small sample sizes, damped exponential family of correlation structure and non-ignorable missing data.
authors.affiliation: Department of Clinical Sciences, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
authors.forename: Song
authors.initials: S
authors.lastname: Zhang
authors.forename: Chul
authors.initials: C
authors.lastname: Ahn
mesh_terms: D002986:Clinical Trials as Topic / Q000379:methods* / Q000706:statistics & numerical data*; D006801:Humans; D008137:Longitudinal Studies; D012107:Research Design / Q000706:statistics & numerical data*; D018401:Sample Size; D013223:Statistics as Topic / Q000379:methods*