A multistate Markov chain model for longitudinal, categorical quality-of-life data subject to non-ignorable missingness
Statistics in Medicine
http://www.ncbi.nlm.nih.gov/pubmed/?term=A%20multistate%20Markov%20chain%20model%20for%20longitudinal%2C%20categorical%20quality-of-life%20data%20subject%20to%20non-ignorable%20missingness.