School of Mathematics and Science, Yancheng Teachers University

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.