Anna Ivanova, Geert Molenberghs, Geert Verbeke, Mechanism for missing data incorporated in joint modelling of ordinal responses, Journal of the Royal Statistical Society. Series C (Applied Statistics) ...

Thomas Lumley, Generalized Estimating Equations for Ordinal Data: A Note on Working Correlation Structures, Biometrics, Vol. 52, No. 1 (Mar., 1996), pp. 354-361 ...

Instead, we develop a multivariate model for ordinal trait analysis and implement an EM algorithm for parameter estimation. We also propose a method for calculating the variance-covariance matrix ...