Testing for Correlation Coefficients in Uniform Correlation Longitudinal Mixed Effect Linear Models Based on M-estimation

In this paper, the Fisher scoring method is applied to get M-estimator (robust estimator) in the mixed effects linear model for longitudinal data. The score tests for correlation coefficients in the model with uniform correlation covariance structure based on M-estimator are also studied. Then the properties of test statistics are investigated through Monte Carlo simulations. At last, the methods and properties are illustrated by the grape sugar data example.