The current meta-analysis investigated the extent to which personality traits changed as a result of intervention, with the primary focus on clinical interventions. We identified 207 studies that had tracked changes in measures of personality traits during interventions, including true experiments and prepost change designs. Interventions were associated with marked changes in personality trait measures over an average time of 24 weeks (e.g., d = .37). Additional analyses showed that the increases replicated across experimental and nonexperimental designs, for nonclinical interventions, and persisted in longitudinal follow-ups of samples beyond the course of intervention. Emotional stability was the primary trait domain showing changes as a result of therapy, followed by extraversion. The type of therapy employed was not strongly associated with the amount of change in personality traits. Patients presenting with anxiety disorders changed the most, and patients being treated for substance use changed the least. The relevance of the results for theory and social policy are discussed. (PsycINFO Database Record

The longitudinal stability of personality is low in childhood, but increases substantially into adulthood. Theoretical explanations for this trend differ in the emphasis placed on intrinsic maturation and socializing influences. To what extent does the increasing stability of personality result from the continuity and crystallization of genetically influenced individual differences, and to what extent does the increasing stability of life experiences explain increases in personality trait stability? Behavioral genetic studies, which decompose longitudinal stability into sources associated with genetic and environmental variation, can help to address this question. We aggregated effect sizes from 24 longitudinal behavioral genetic studies containing information on a total of 21,057 sibling pairs from six types that varied in terms of genetic relatedness and ranged in age from infancy to old age. A combination of linear and nonlinear meta-analytic regression models were used to evaluate age-trends in levels of heritability and environmentality, stabilities of genetic and environmental effects, and the contributions of genetic and environmental effects to overall phenotypic stability. Both the genetic and environmental influences on personality increase in stability with age. The contribution of genetic effects to phenotypic stability is moderate in magnitude and relatively constant with age, in part because of small-to-moderate decreases in the heritability of personality over child development that offset increases in genetic stability. In contrast, the contribution of environmental effects to phenotypic stability increases from near-zero in early childhood to moderate in adulthood. The lifespan trend of increasing phenotypic stability, therefore, predominantly results from environmental mechanisms.

Genes account for between approximately 50% and 70% of the variation in cognition at the population level. However, population-level estimates of heritability potentially mask marked subgroup differences. We review the body of empirical evidence indicating that (a) genetic influences on cognition increase from infancy to adulthood, and (b) genetic influences on cognition are maximized in more advantaged socioeconomic contexts (i.e., a Gene × Socioeconomic Status interaction). We discuss potential mechanisms underlying these effects, particularly transactional models of cognitive development. Transactional models predict that people in high-opportunity contexts actively evoke and select positive learning experiences on the basis of their genetic predispositions; these learning experiences, in turn, reciprocally influence cognition. The net result of this transactional process is increasing genetic influence with increasing age and increasing environmental opportunity.

The longitudinal rank-order stability of cognitive ability increases dramatically over the lifespan. Multiple theoretical perspectives have proposed that genetic and/or environmental mechanisms underlie the longitudinal stability of cognition, and developmental trends therein. However, the patterns of stability of genetic and environmental influences on cognition over the lifespan largely remain poorly understood. We searched for longitudinal studies of cognition that reported raw genetically-informative longitudinal correlations or parameter estimates from longitudinal behavior genetic models. We identified 150 combinations of time points and measures from 15 independent longitudinal samples. In total, longitudinal data came from 4,538 monozygotic twin pairs raised together, 7,777 dizygotic twin pairs raised together, 34 monozygotic twin pairs raised apart, 78 dizygotic twin pairs raised apart, 141 adoptive sibling pairs, and 143 non-adoptive sibling pairs, ranging in age from infancy through late adulthood. At all ages, cross-time genetic correlations and shared environmental correlations were substantially larger than cross-time nonshared environmental correlations. Cross-time correlations for genetic and shared environmental components were low during early childhood, increased sharply over child development, and remained relatively high from adolescence through late adulthood. Cross-time correlations for nonshared environmental components were low across childhood and increased gradually to moderate magnitudes in adulthood. Increasing phenotypic stability over child development was almost entirely mediated by genetic factors. Time-based decay of genetic and shared environmental stability was more pronounced earlier in child development. Results are interpreted in reference to theories of gene-environment interaction and correlation.

Past research syntheses provided evidence that personality traits are both stable and changeable throughout the life span. However, early meta-analytic estimates were constrained by a relatively small universe of longitudinal studies, many of which tracked personality traits in small samples over moderate time periods using measures that were only loosely related to contemporary trait models such as the Big Five. Since then, hundreds of new studies have emerged allowing for more precise estimates of personality trait stability and change across the life span. Here, we updated and extended previous research syntheses on personality trait development by synthesizing novel longitudinal data on rank-order stability (total k = 189, total N = 178,503) and mean-level change (total k = 276, N = 242,542) from studies published after January 1, 2005. Consistent with earlier meta-analytic findings, the rank-order stability of personality traits increased significantly throughout early life before reaching a plateau in young adulthood. These increases in stability coincide with mean-level changes in the direction of greater maturity. In contrast to previous findings, we found little evidence for increasing rank-order stabilities after Age 25. Moreover, cumulative mean-level trait changes across the life span were slightly smaller than previously estimated. Emotional stability, however, increased consistently and more substantially across the life span than previously found. Moderator analyses indicated that narrow facet-level and maladaptive trait measures were less stable than broader domain and adaptive trait measures. Overall, the present findings draw a more precise picture of the life span development of personality traits and highlight important gaps in the personality development literature. Public Significance StatementThis study summarized data from hundreds of longitudinal studies to confirm that (a) personality trait differences are fairly stable among adults, (b) these differences tend to stabilize during adolescence and young adulthood, and (c) personality tends to change in the direction of greater maturity as people age. These patterns hold across gender, nation, and ethnicity, although research from Western countries was overrepresented.