Simultaneous Models for Contingency Tables: A Reanalysis of Heatherton et al. (1997) Data on Eating Behavior

In panel studies, where a categorical response is measured attwo points in time, we can examine two kind of hypotheses regardingthe nature of change. The first is related with change at theindividual level (gross change) through the modelling of joint distributionof responses. The second is related with aggregate change (netchange) through the modelling of marginal distributions of responses.This paper describes a general approach to the analysis of two-wavepanel data based on Lang and Agresti's work (1994) that simultaneouslypermits the modelling of marginal and joint distributions of responses.This approach is illustrated with data from Heatherton et al.(1997) about change in dieting behaviour. These data were originallyanalyzed using the ² statistic to test independenceof responses. This paper shows how it is possible toobtain a better understanding of these data using the proposedmethodological approach.