The Cumulative Continuity Model of Personality Development: Striking a Balance Between Continuity and Change in Personality Traits across the Life Course

Abstract

Research has shown that personality-trait consistency is more common than personality-trait change and that when personality-trait change occurs, it is seldom dramatic. This finding results in a theoretical dilemma, for trait theories provide no explanation for personality change. Alternatively, most theories of adult developmental focus on change but not change in personality traits. To address this theoretical oversight, we first describe the mechanisms that promote personality continuity, such as the environment, genetic factors, psychological functioning, and person-environment transactions. Then we describe the counterpart to continuity, the mechanisms that facilitate personality change, such as responding to contingencies, observational learning, learning generalization, and learning from others' descriptions of ourselves. We argue that identity processes can explain both the mechanisms of continuity and change and form the basis for a theory that explains the empirical findings on personality-trait development over the life course. Specifically, we make the case that the development of a strong identity and certain facets of identity structure, such as identity achievement and certainty, are positively related to many of the mechanisms that promote personality continuity. Furthermore, we argue that one unintentional consequence of identity development is to put oneself into contexts that promote personality change, such as new roles or a different circle of friends. Over the last several decades, the topic of personality-trait development has led a quixotic existence that paralleled the fortunes of the field of personality psychology in general. With Mischel's (1968) behaviorist critique of traits, the study of personality-trait development was left focused on social and environmental causes of both consistency and change. It was common in the late 1960s and early 1970s for authors to assume that traits were not consistent and, if they were, to attribute all of the consistency to environmental consistency (e.g., Nesselroade & Baltes, 1974). In the ensuing years, numerous longitudinal studies of personality yielded impressive evidence for the continuity of personality, and the field moved rapidly past the moderate position that there is both continuity and change in traits in adulthood (e.g., Kogan, 1990), to the extreme position that personality traits become "fixed" in young adulthood and remain unchanging thereafter (McCrae & Costa, 1994). This "strong stability" position precludes the idea that personality traits continue to develop in adulthood and, if accepted, effectively preempts the study of adult personality-trait development altogether. Neither the extreme environmental argument nor the strong stability argument is justified given the empirical evidence. For example, despite the impression given by Mischel's (1968) critique of personality traits and the ensuing person-situation debate (Kenrick & Funder, 1988), the evidence for the consistency of personality traits across time was always compelling. As long ago as 1941, Crook compiled data from six longitudinal studies showing that trait consistency averaged above.80 over several weeks and dropped to around.50 after six and a half years. Subsequent reviews using anywhere from 20 to 152 longitudinal studies of personality consistency have replicated Crook's findings (Conley, 1984; Roberts & DelVecchio, 2000; Schuerger, Zarrella, & Hotz, 1989). Studies of the longitudinal consistency of traits also have shown that one of the most profound moderators of consistency is the age of the sample being studied (Caspi & Roberts, 1999; Finn, 1986; Roberts, Helson, & Klohnen, 2002). For example, in a review of 152 longitudinal studies, Roberts and DelVecchio (2000) showed that estimates of personality consistency (unadjusted for measurement error) increased from.31 in childhood, to.54 during the college-age period, to.64 at age 30, and then reached a plateau near.74 between ages 50 and 70 (over an average span of seven years). Complementing the robust evidence for the relatively enduring nature of personality traits is the evidence for change in personality continuing well past young adulthood. Studies that examine change in personality traits find an increase or decrease in mean levels across most age periods (Dudek & Hall, 1991; Field & Millsap, 1991; Finn, 1986; Helson & Moane, 1987; Leon, Gillum, Gillum, & Gouze, 1979; Nilsson & Persson, 1984; Roberts, Helson, & Klohnen, 2002; Stevens & Truss, 1985). Furthermore, individual differences in personality-trait change exist at most ages (Jones & Meredith, 1996) and are related to life experiences in young adulthood (Pals, 1999), midlife (Roberts, 1997; Roberts & Chapman, 2000), and old age (Tower & Kasl, 1996). It should be noted that the effect sizes associated with trait consistency usually exceed.50, while the effect sizes for mean-level change and individual differences in change are much smaller in magnitude. The picture that emerges from the longitudinal evidence for personality development leads to several conclusions. First, personality traits are highly consistent compared to other psychological constructs and are exceeded in consistency only by measures of cognitive ability (e.g., Conley, 1984). Second, personality consistency increases with age and yet may never reach a level high enough to indicate that personality traits stop changing. Third, according to mean-level and individual-difference approaches, personality change can and does occur even into old age. The picture one draws from the empirical data seems eminently reasonable: personality traits increase in consistency as people age, reaching levels that are quite high but not so high as to rule out the possibility or reality of meaningful shifts in traits over time. Unfortunately, this temperate perspective on personality-trait development across the life course is not captured well in the existing theories of personality and adult development. In his review of personality and aging, Kogan (1990) highlighted three theoretical approaches to personality development. The first model is the classical psychometric theory or trait model of personality development (see also Conley, 1985). According to this perspective, traits remain so stable in adulthood that they are essentially "temperaments" and are impervious to the influence of the environment (e.g., McCrae & Costa, 1994; McCrae et al., 2000). The second model, termed the contextual model (Lewis, 1999), reflects the perspective that personality traits are shaped by environmental contingencies often contained within social roles (Brim, 1965). This perspective emphasizes the flux and change of personality and can only assume that personality consistency results from the consistency of social environments—a relatively weak and primarily untested argument. The third model is centered on the stage theories of Erikson (1950) and Levinson (1986), both of whom emphasize the change and emergence of specific life tasks and associated crises at different ages. This perspective essentially ignores personality-trait development. Taken separately, each of these three perspectives on personality development is lacking in some fundamental way. Classical psychometric trait theories beg the question of developmental process by defining personality as only that component of human nature that does not change—in our opinion a small and possibly uninteresting portion of human nature. Contextual models choose to ignore the genetic and psychological mechanisms that promote continuity and provide often overly optimistic perspectives on the mutability of personality (see also Cloninger, this volume). The stage models of adult development focus on important topics—the development of social roles and identity—but fail to incorporate these ideas with the prevailing evidence that differences in personality exist and are stable despite or because of development of social roles and identity structures. We would add the lifespan development approach as a fourth model, which proposes a dialectic between consistency and change over the life course. The lifespan perspective comes closest to approximating the empirical picture of personality-trait development in that it specifies quite clearly that people are open systems and that they exhibit both continuity and change in personality throughout the life course (see also Lerner, Dowling, & Roth, this volume). Furthermore, according to the lifespan model, the effects of psychological, social, and cultural factors diminish as people grow older, often as a result of selection, optimization, and compensation processes (Baltes, Lindenberger, & Staudinger, 1999; see also Smith, this volume). In the present chapter, we seek to expand on the lifespan model and set down the central tenets of the cumulative continuity model of personality development. Unlike previous conceptualizations of personality development, the cumulative continuity model attempts to integrate the findings of empirical research on the development of personality traits with the theoretical and empirical models derived from identity research in an attempt to explain the patterns of personality-trait continuity and change across the life course. In this effort, we attempt to integrate personality-trait development and identity development with perspectives derived from lifespan models (Baltes, Lindenberger, & Staudinger, 1999; Brandtstädter & Greve, 1994). We begin our argument under the assumption that the empirical data to date are accurate. That is, personality traits increase in consistency with age, are mostly consistent in adulthood, and yet retain the capacity for change throughout the adult life course. If one accepts these data, several questions arise: First, why are personality traits consistent? We can no longer simply assume, as is done in the classical psychometric model, that personality traits are stable and that stability needs no explanation (Nesselroade & Featherman, 1997). In the first section below, we address the mechanisms that promote continuity in personality traits. The second question that arises is, what are the mechanisms that facilitate personality-trait change in adulthood? We address this question in the second section. Third, why do personality traits change less as people age and yet still retain some plasticity? In the last section, we answer this question by putting forward the argument that identity development and structures of identity mediate between personality traits and the mechanisms of change and continuity and that the mediating role of identity helps to explain, in part, the patterns of continuity and change in personality traits across the life course.