Because frequently random assignment is not feasible in educational studies, our understanding of causal effects of student characteristics on academic performance has made little progress over the years. Omitted variables inducing correlations between regressors and error terms in multilevel...

We develop a general class of factor-analytic models for the analysis of multivariate (truncated) count data. Dependencies in multivariate counts are of interest in many applications, but few approaches have been proposed for their analysis. Our model class allows for a variety of distributions...

Multivariate count data are commonly analysed by using Poisson distributions with varying intensity parameters, resulting in a random-effects model. In the analysis of a data set on the frequency of different emotion experiences we find that a Poisson model with a single random effect does not...

Our comments about the paper by Leeflang and Wittink wInternat. J. Res. Marketing, 17 2000. 105x comprise of two components: first, we address two issues on which we disagree with Leeflang and Wittink: soft versus hard data, and individual-level versus segment-level models. Secondly, we...