INTRODUCTION

Research focus

A salient aspect of research on adult development and aging is the use of general dimensions of interindividual differences to classify elderly persons into diagnostic groups, to predict longevity, morbidity, mortality, and other conditions, and to theorize about the nature of development and change. Among the more prominent variables that social and behavioral scientists are using currently for these purposes are measures of morale, life satisfaction, autonomy and control, adjustment, and depression. Of these, depression has become a major focus of concern because of both its probable association with the variety of losses that older adults are apt to experience (spouse, job, status, health, etc.) and its mediating role between the onset of traumatic events and the person's subsequent adaptation. An aspect of research conducted with depression and other relatively broad interindividual differences dimensions that has yet to be integrated into either theoretical or methodological concerns generally are the various phenomena of intraindividual variability or short-term changes.

Although greater and greater levels of sophistication in measurement, research design, and data analyses are being reached in longitudinal approaches (see, e.g., Goldstein, 1979; Nesselroade & Bakes, 1979; Schaie, Campbell, Meredith & Rawlings, 1988), many promising ideas and innovations do not readily filter into substantive research efforts. An encouraging conception and accompanying set of findings that researchers in adult development and aging have not yet sufficiently taken into account concern the nature, scope, and correlates of intraindividual variability and the implications that arise therefrom both for explanatory purposes and for the classification and prediction objectives mentioned above (Nesselroade, 1990).