ABSTRACT
This chapter traces the evolution on how to design studies that will characterize developmental progressions with minimal conceptual ambiguity. It reviews with the realization that data on the adult development of mental abilities showed wide discrepancies between cross-sectional and longitudinal data collected on the same subject population over a wide age range. The chapter examines some of the characteristics of the general developmental model, review how the strategies derived therefrom relate to non-developmentally oriented prescriptions for quasi-experiments; describe an optimal data collection approach. It attempts to explain the discrepancies by constructing a general model for the study of developmental change that explicated the relationships between the cross-sectional and longitudinal methods. Planned design misspecifications are useful also for the estimation of lower-bound estimates of developmental components. Examination of developmentally oriented data bases then suggested that the traditional cross-sectional and longitudinal approaches as well as the newly defined time-lag alternative are simply special cases of the model.
