Some Methodological Issues in Developmental Research

Abstract

Developmental psychology can be defined as the systematic study of mental and behavioural development in humans. Its concern is to understand those changes in ability and behaviour which are associated with increasing age. The task of the developmental psychologist, therefore, is to specify the nature of the psychological processes underlying age-related changes in ability and behaviour. The task, in effect, is a twofold one: firstly, to identify and describe developmental phenomena—changes in behaviour occurring along the dimension of age—and, secondly, to provide an explanatory account of the phenomena thus identified. It bears stressing in this context that age itself cannot be regarded as an explanatory variable; growing older does not cause behavioural change. Ten-year-old children can do many things that five-year-olds cannot, but the explanation for this does not lie in the fact that the formér are five years older than the latter. Chronological age is simply a convenient way of measuring the passage of time since birth, but the mere passage of time does not explain behavioural change. It is for this reason that age is sometimes referred to as a carrier or index variable, a dimension within which the processes which do cause behavioural development may be located. These processes—experiential, maturational, physiological—co-vary with increasing age simply because they require time in which to occur. Ultimately, however, explanations for developmental phenomena are sought in terms of the variables which moderate the course of the changes in ability and behaviour that are observed to take place with increasing age. It is with some of the methodological issues which arise in the study of age-related changes in behaviour that this chapter is concerned.