關鍵字:IIS性質，線性混合模式，長期追蹤資料。 Classical group sequential methods are based on the assumption of independent increments structure (IIS) between the interim test statistics. Three common classical group sequential methods are proposed by Pocock(1977), O''Brien and Fleming(1979), and Lan and DeMets(1983). However, for longitudinal data the IIS assumption between the interim test statistics does not hold because of the correlation between the measurements from the same subject. Several parametric methods of group sequential test for analyzing the data with repeated measurements or multiple observations have been developed by Armitage et al.(1985), Geary(1988), Tang et al.(1989) and Lee and DeMets(1991). The proposed quadratic form test statistic is a generalization of Lee and DeMets'' statistic to polynomial setting. The sampling distributions of the proposed test statistic at each stage as well as the joint distribution are discussed by simulation studies. The proposed testing procedure is illustrated by a clinical example.