ANALYSIS OF REPEATED CATEGORICAL-DATA USING GENERALIZED ESTIMATING EQUATIONS

Moment methods for analysing repeated binary responses have been propo sed by Liang and Zeger, and extended by Prentice and Zhao and Prentice . In these estimating equations, models are proposed for the correlati on between the repeated binary responses. We extend Liang and Zeger's method to models for the correlation between repeated nominal or ordin al categorical responses; in particular, when the repeated responses a re binary, our methods reduce to Liang and Zeger's method. Our method is illustrated with two datasets. One dataset contains repeated observ ations of self-assessment of arthritis, an ordered variable with three categories, collected during a randomized comparative study of altern ative treatments of patients with rheumatoid arthritis. The second dat aset is a longitudinal study of the health effects of air pollution, i n which the repeated ordered multinomial response is the wheezing stat us (no wheeze, wheeze with cold, wheeze apart from cold) of a child at ages 9, 10, 11 and 12 years.