Abstract
This essay considers progress in understanding adult development in the study of behaviour during the 20th century. It describes the influence of methodological advances including paradigmatic shifts from cross-sectional to longitudinal studies, advances in measurement, the impact of confirmatory factor analysis, and consideration of age as the dependent variable. A theoretical framework for understanding adult cognitive development is presented. Different types of longitudinal studies, the issue of structural invariance across age, sources of individual differences and the impact of cohort differences are discussed. Finally projections are made for future research.
