PersonalityTrait Changes Among Young Finns:The Role of Life Events and Transitions Sointu Leikas 1 and Katariina Salmela-Aro 1,2 1 University of Helsinki 2 University of Jyväskylä Abstract Recent research has shown that personality traits continue to develop throughout the life span,but most profound changes are typically found during young adulthood.Increasing evidence suggests that life events play a significant role in many of these changes. The present longitudinal study examined the role of work, education, social, and health-related life events in the development of the Big Five traits among young Finns.Participants were originally recruited in 2004 through elementary schools in a middle-sized Finnish city. Participants’ Big Five traits and life events were measured via self-reports at ages 20 and 23 (Ns = 597 and 588, respectively). Entering work life, beginning a relationship, and studying in university predicted increases in Conscientiousness, trying drugs predicted increases in Neuroticism, and onset of a chronic disease predicted increases in Neuroticism and Conscientiousness between ages 20 and 23.The results suggest that mature life transitions relate to stronger increases in Conscientiousness in young adulthood,and that non-normative life choices and events may predict increases in Neuroticism. Questions concerning personality continuity and change have long been among the most central ones in the behavioral sci- ences. The traditional view of trait psychology has highlighted strong personality consistency in adulthood (e.g., McCrae & Costa, 1999). However, the results of several recent longitudi- nal studies and meta-analyses (e.g., Helson, Jones, & Kwan, 2002; Roberts, Caspi, & Moffitt, 2003; Roberts & DelVecchio, 2000; Robins, Fraley, Roberts, & Trzesniewski, 2001; Roberts, Walton, & Viechtbauer, 2006) suggest that personality is, throughout the life span, more changeable than was previously assumed. Furthermore, personality development seems to be intertwined with social development, role transitions, chang- ing environments, and life events (e.g., Lehnart, Neyer, & Eccles, 2010; Roberts et al., 2003; Roberts, Wood, & Caspi, 2008; Specht, Egloff, & Schmukle, 2011). Why and how does personality change? The essentialist view sees personality change as the result of maturation guided by genetic factors (Costa & McCrae, 2006; McCrae et al., 2000), but the existing data do not fully support this view (e.g., Roberts, Wood, & Smith, 2005). Thus, the environment may also play a role in personality change. However, researchers have only begun to explore the ways through which environ- mental factors such as life experiences might affect personality change (e.g., Jackson, Thoemmes, Jonkmann, Lüdtke, & Trautwein, 2012; Lüdtke, Roberts, Trautwein, & Nagy, 2011; Specht et al., 2011). But which events play a role in the changes of which traits? Can normative social role changes partly explain normative personality changes (i.e., changes that describe all or most individuals at a certain age)? Why do some individuals change in non-normative ways? The present longitudinal study aims to shed some light on the above described questions by examining the moderating effects of both normative and non-normative life events on change in the Big Five personality traits during the transition to adulthood. Personality Change Personality change comes in many forms (e.g., Roberts et al., 2008). In the present research, we focus on two of the most common forms of change: mean-level change and rank-order change (vs. stability). Mean-level change refers to changes in trait levels over time at a group level (e.g., Roberts, Walton, & Viechtbauer, 2006). For instance, a group of people followed from ages 18 to 30 typically receives, at the group level, higher mean scores of Conscientiousness at the latter than at the former assessment (e.g., Helson, Jones, et al., 2002; Roberts, Caspi, & Moffitt 2001; Robins et al., 2001). A recent meta- analysis on the mean-level change of the Big Five personality traits showed that mean-level changes occur throughout the life span for all five traits (Roberts, Walton, & Viechtbauer, 2006). However, Roberts, Walton, and Viechtbauer (2006) Correspondence concerning this article should be addressed to Sointu Leikas, P.O. Box 9, Siltavuorenpenger 1 A, 00014 University of Helsinki, Helsinki, Finland. Email: sointu.leikas@helsinki.fi. Journal of Personality 83:1, February 2015 © 2014 Wiley Periodicals, Inc. DOI: 10.1111/jopy.12088