INTERNATIONAL JOURNAL OF BEHAVIORAL DEVELOPMENT, 1989,12 (1) 1-34 Age as an Ambiguous Variable in Developmental Research: Some Epidemiological Considerations from Developmental Psychopathology

Intra-individual change in behaviour with age constitutes the essential ele-ment in developmental research but, unless age is broken down into its component parts, age is devoid of meaning. The issues involved are dis-cussed from the perspective of epidemiology as applied to developmental psychopathology. Methodological concerns are discussed with respect to continuities and discontinuities in development (with special reference to the cumulative emergence of skills and variable consistency over the life span), secular trends, and the distinction between individual and group-aggregated age trends. The different components of chronological age are considered in terms of cognitive level, different types of biological maturity, and the duration of type of life experiences. The same components are discussed with respect to the issues involved in the study of differential effects of experiences according to their timing in the developmental se-quence, and maturational delay