Quality & Quantity 35: 351–363, 2001.
© 2001 Kluwer Academic Publishers. Printed in the Netherlands.
Simultaneous Models for Contingency Tables: A
Reanalysis of Heatherton et al. (1997) Data on
MARÍA F. RODRIGO
Departamento de Metodología, Facultad de Psicología, Universidad de Valencia, Avda. Blasco
Ibáñez, 21, 46010-Valencia, Spain. E-mail: Maria.F.Rodrigo@uv.es
MANUEL ATO and RAFAEL RABADAN
Departamento de Psicología Básica y Metodología, Facultad de Psicología, Universidad de
Murcia, Apartado 4021, 30080-Murcia, Spain
Abstract. In panel studies, where a categorical response is measured at two points in time, we can
examine two kind of hypotheses regarding the nature of change. The ﬁrst is related with change
at the individual level (gross change) through the modelling of joint distribution of responses. The
second is related with aggregate change (net change) through the modelling of marginal distributions
of responses. This paper describes a general approach to the analysis of two-wave panel data based
on Lang and Agresti’s work (1994) that simultaneously permits 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 originally analyzed using the χ
statistic to test inde-
pendence of responses. This paper shows how it is possible to obtain a better understanding of these
data using the proposed methodological approach.
Key words: categorical data, simultaneous modelling, marginal models, panel studies
Panel studies where the outcome is an ordered or unordered categorical response
occur frequently in behavioural research. Panel studies present an interesting area
for the analysis of categorically-scored data, since such data allow us to test hy-
potheses about the nature of change. With measurements taken at t points in time
data can be arranged in a t-way contingency square table.
An illustrative example of a panel study with ordered categorical responses is a
10-year longitudinal study of eating behaviour and eating disorder symptoms from
Heatherton et al. (1997). This study focuses on stability and change during the
transition to adulthood using a cohort who were teenagers in the late 1970s and
early 1980s and who were contacted again 10 years after their original particip-
ation. Tables I and II present a cross-classiﬁcation of 502 women and 205 men,
respectively, who reported dieting behaviour in 1982 and 1992.