Likelihood Ratio Testing for Zero Variance Components in Linear Mixed Models.

Mixed models are a powerful inferential tool with a wide range of applications including longitudinal studies, hierarchical modeling, and smoothing. Mixed models have become the state of the art for statistical information exchange and correlation modeling. Their popularity has been augmented by the availability of dedicated software, e.g., the Mixed procedure in SAS, the lme function in R and S², or the xtmixed f un c t i on i n STATA. [ABSTRACT FROM AUTHOR]