Different theories make different predictions about how mean levels of personality traits change in adulthood. The biological view of the Five-factor theory proposes the plaster hypothesis: All personality traits stop changing by age 30. In contrast, contextualist perspectives propose that changes should be more varied and should persist throughout adulthood. This study compared these perspectives in a large (N = 132,515) sample of adults aged 21– 60 who completed a Big Five personality measure on the Internet. Conscientiousness and Agreeableness increased throughout early and middle adulthood at varying rates; Neuroticism declined among women but did not change among men. The variety in patterns of change suggests that the Big Five traits are complex phenomena subject to a variety of developmental influences.

How does personality change during adulthood? Psychologists since William James (1890/1950) have struggled with the question of whether various aspects of personality, including personality traits, change in meaningful ways during adulthood, and when those changes take place. Contemporary hypotheses about the development of personality traits stem from theories about what personality traits are. McCrae and Costa’s (1996) five-factor theory asserts that personality traits arise exclusively from biological causes (i.e., genes) and that they reach full maturity in early adulthood; thus, this theory predicts little or no change on any personality dimension after early adulthood. By contrast, contextualist perspectives argue that traits are multiply determined, and that one important influence on traits is the individual’s social environment (Haan, Millsap, & Hartka, 1986; Helson, Jones, & Kwan, 2002). Contextualist perspectives thus predict plasticity: Change is complex and ongoing, owing to the many factors that can affect personality traits. In this study, we set out to understand how personality traits change in early and middle adulthood by examining the Big Five personality trait dimensions (Goldberg, 1992; John & Srivastava, 1999; McCrae & Costa, 1999). We used a cross-sectional design to study how mean levels of personality traits differ by age and whether those age effects are moderated by gender.(1) We were particularly interested in examining whether change on all of the Big Five dimensions stops or slows in middle adulthood, as predicted by the five-factor theory, or whether change is ongoing and differentiated, as predicted by contextualist theories.

Past Research on Mean-Level Change on the Big Five During Adulthood
A recent literature review summarized previous studies of mean-level change on the Big Five (Roberts, Robins, Caspi, & Trzesniewski, in press). In this review, Roberts et al. (in press) rationally categorized a wide variety of personality measures into the Big Five domains and summarized patterns of mean-level change that were consistent across studies. They concluded that, in general, Conscientiousness and Agreeableness tend to go up during adulthood, Neuroticism tends to go down, Openness shows mixed results across studies, and Extraversion shows no general pattern of change at the factor level. This basic pattern of findings has been reported in specific studies by researchers who argue that personality traits are affected by context (e.g., Helson et al., 2002; Helson & Kwan, 2000) as well as those who favor a strictly biological interpretation of traits (e.g., McCrae et al., 1999, 2000).
Although Roberts et al.’s (in press) conclusion seems to represent some common ground among researchers, there is still considerable disagreement: The biological and contextual perspectives disagree sharply over the timing of changes within the life course and over whether there are any differences between men’s and women’s development.

Set Like Plaster: The Five-Factor Theory
According to the five-factor theory, personality traits are “insulated from the direct effects of the environment” (McCrae & Costa, 1999, p. 144) and are exclusively biological in origin. Change is addressed by Postulate 1c of the five-factor theory: “Traits develop through childhood and reach mature form in adulthood; thereafter they are stable in cognitively intact individuals” (McCrae & Costa, 1999, p. 145). More specifically, traits are said to reach maturity by age 30 (e.g., Costa & McCrae, 1994; McCrae & Costa, 1999; McCrae et al., 2000). The predicted stability is expected to last throughout middle age, though in old age personality could change again, being disrupted by cognitive decline. A commonly used metaphor for this pattern of change, based on a passage from William James (1890/1950), is that personality becomes “set like plaster” by age 30 (see Costa & McCrae, 1994); thus, we refer to Postulate 1c, in its general form, as the plaster hypothesis.
In its original formulation, the plaster hypothesis stated that changes in Big Five traits after age 30 were nonexistent or trivial (Costa & McCrae, 1994; McCrae & Costa, 1990, 1996). More recently, the authors of the five-factor theory have indicated that the plaster hypothesis is “ripe for minor revision” (McCrae & Costa, 1999, p. 145), as studies have shown changes in mean levels of personality traits after age 30 (e.g., McCrae et al., 1999, 2000; see also Roberts et al., in press). They interpret such changes as stemming from intrinsic biological maturation rather than social influences, and they still regard the plaster hypothesis as basically true: “From age 18 to age 30 there are declines in Neuroticism, Extraversion, and Openness to Experience, and increases in Agreeableness and Conscientiousness; after age 30 the same trends are found, although the rate of change seems to decrease” (McCrae et al., 2000, p. 183). Despite this conclusion, no study that we are aware of has directly tested whether mean levels of the Big Five traits do in fact change less after age 30 than before. This may be in part because past research on adult development has compared discrete age groups, rather than treating age as a continuous variable. For example, McCrae et al.’s (1999, 2000) two recent cross-sectional studies reported means for groups of 22- to 29-year-olds and means for groups of 30- to 49-year-olds, but the studies do not report the amount of change within those critical age ranges. We thus set out to test the plaster hypothesis by directly comparing rates of change during the relevant age periods. In translating the plaster hypothesis into formal predictions about rates of change, we specified two versions of it. We call the original formulation (as described in Costa & McCrae, 1994) the hard plaster hypothesis: Age effects after age 30 should not be reliably different from zero, and this should hold for each of the Big Five dimensions. We call the more recent “minor revision” (McCrae & Costa, 1999) the soft plaster hypothesis, because here personality is like plaster that has not fully hardened but is becoming more and more viscous: Personality traits change more slowly after age 30 than before age 30.

(1) “Change” is a broad concept that can be defined in a variety of other ways, such as rank-order change (whether people change in their ordering relative to age mates) and individual differences in change (whether different individuals change at different rates over time). These other ways of examining change address somewhat different substantive issues, and it is possible to obtain conceptually compatible but different results with the different approaches. (For a fuller discussion of different kinds of change, see Caspi & Roberts, 1999.)

Continua >>>>>

Scarica l'intero testo .pdf (126 Kb)