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Point estimation after early stopping in a repeated measures trial
Authors:Jae Won Lee  Mira Park
Affiliation:1. Department of Statistics , Korea University , 136–701, Seoul, South Korea , 5–1 Anam -dong, Sungbuk-gu;2. Department of Premedicine , Eulji Medical College , 301–112, South Korea , 43–5 Yongdu -dong, Chung- ku , Taejon
Abstract:
When the individual measurements are statistically independent, the maximum likelihood estimator calculated at the end of a sequential procedure overestimates the underlying effect. There are many clinical trials in which we are interested in comparing changes in responses between two treatment groups sequentially. Lee and DeMets (1991, JASA 86, 757–762) proposed a group sequential method for comparing rates of change when a response variable is measured for eaeh patient at successive follow-up visits. They assumed that the response follows the linear mixed effects model and derived the asymptotic joint distribution of the sequentially computed statistics. In this article, we consider the maximum likelihood estimator (MLE), the median unbiased estimator (MUE) and the midpoint of a 100(1-α)% confidence interval as point estimators for the rate of change in the linear mixed effects model, and investigate their properties by Monte Carlo simulation.
Keywords:Group sequential testing  Repeated measurements  Rates of changes
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