Trait stability and maturation are fundamental principles of contemporary personality psychology and have been shown to hold across many cultures. However, it has proven difficult to move beyond these general findings to a detailed account of trait development. There are pervasive and unexplained inconsistencies across studies that may be due to (a) insufficient attention to measurement error, (b) subtle but age-sensitive differences in alternative measures of the same trait, or (c) different perspectives reflected in self-reports and observer ratings. Multiscale, multimethod—and ideally multinational—studies are needed. Several hypotheses have been proposed to account for trait stability and change, but supporting evidence is currently weak or indirect; trait development is a fertile if sometimes frustrating field for theory and research. Beyond traits, there are approaches to personality development that are of interest to students of adult development, and these may be fruitfully addressed from a trait perspective.

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