Studying human development involves describing, explaining, and optimizing intraindividual change and interindividual differences in such change and, as such, requires longitudinal research. The selection of the appropriate type of longitudinal design requires selecting the option that best addresses the theoretical questions asked about…

An examination of the concept of external validity from two theoretical perspectives: a traditional mechanistic approach and a dialectical organismic approach. Examines the theoretical and methodological implications of these perspectives. (BD)

Problems in making inferences from a sample to a population and from one cohort to other cohorts are discussed. It is concluded that in most cases a longitudinal design using repeated measures is preferable to an independent samples design. (Author)

Describes the use of simulated time sequences in the analysis of age-related and socio-historical changes in developmental research. (BD)

Evaluates empirical studies on child development. Suggests that most such research consists of studies of a priori, nonempirical, logical relations between concepts, whose definitions guarantee the relationship studied. Argues that hypotheses are empirical if variables involved are semantically and logically independent. Research that is not based…

Five symposium papers evaluate the usefulness of ideas associated with the life-span view for enriching, highlighting, or expanding issues, theory, and research pertinent to change processes during infancy, childhood, adolescence, and adulthood, and for intervention programs during these periods. (Author/MP)

Comments on the ideas espoused by Smedslund (PS 522 552) in this issue. Agrees to the idea of spending more intellectual energy in distinguishing between a priori and empirical hypotheses but emphasizes that concepts are not always accurate reflections of reality and that even empirical disconfirmation of an a priori hypothesis sometimes can…