INTRODUCTION

The aim of the present chapter is twofold: on the one hand, qualitative analyses of individual developmental trajectories in cognition are presented; on the other hand, conceptual, methodological and statistical implications of the qualitative analysis of individual differences in intraindividual change are discussed. In contrast to the variable-oriented approaches most often applied in the analysis of individual development, a person- or individual-oriented approach will be used (Magnusson, 1985; Schröder, 1989). Person- or individual-oriented approaches are applied in clinical case studies, medical research and biostatistics, where the individual's patterns of characteristics, attributes or trajectories over time are the unit of analysis. This approach thus focuses mainly on configurations or constellations of attributes. In developmental research the individual-oriented approach is infrequent in spite of the fact that the empirical evaluation of important theories about development depends on the analysis of individual paths of development. Thus, for example, Piaget's theory of cognitive development postulates different stages or levels in cognitive development and that certain levels of cognitive functioning always precede, and are a necessary condition for, the emergence of subsequent levels of development (invariable developmental sequence). Empirically, questions concerning décalages in development and developmental sequences can be adequately evaluated only on the basis of the individual developmental patterns, since aggregate developmental curves for groups do not show how the individual develops over time (Bakan, 1967). Therefore, in this chapter we will use an analytical and methodological approach that is designed for the analysis of sequential data, in particular for the study of intraindividual change and intraindividual differences in development.