The question of stability and change is one of the most important in personality and is perhaps the most fundamental question in the area of personality development. Over the past 25 years, researchers have established that rank-order stability is high for most traits (Costa & McCrae, 1988, 1994; Roberts & DelVecchio, 2000), although mean-level stability varies by trait (McCrae & Costa, chap. 7 in this volume). In other types of personality variables (self-efficacy, goals, motives), there is less rank-order and mean-level stability (Helson, Soto, & Cate, chap. 17 in this volume). However, the techniques typically employed to estimate rank-order and mean-level stability in personality variables (or any other type of variable) conceal important information on individual differences. Personality psychology is strongly identified with the science of individual differences, yet it has overlooked the possibility of individual differences in stability and change. Almost 30 years ago, life-span developmentalists advocated the idea of individual differences in intraindividual change (Baltes, Reese, & N esselroade, 1977), but it remained a largely theoretical notion until statistical techniques were invented in the 1980s that permitted adequate testing of this concept (Bryk & Raudenbush, 1992; Rogosa, Brandt, & Zimowski, 1982). As a result, a much more complex, and more accurate, way of con-more ceptualizing stability and change in personality is now available. This chapter discusses these techniques and how they can advance the conceptual science of personality development.
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