We propose a U-statistics-based test for null variance components in linear mixed models and obtain its asymptotic distribution (for increasing number of units) under mild regularity conditions that include only the existence of the second moment for the random effects and of the fourth moment...

In clinical research, study subjects may experience multiple events that are observed and recorded periodically. To analyze transition patterns of disease processes, it is desirable to use those multiple events over time in the analysis. This study proposes a multi-state Markov model with...