264 III. DEvELOPMENT
a form of conscientiousness, and decreased 
notably in neuroticism as they transitioned 
from adolescence to young adulthood (Don -
nellan, Conger, & Burzette, 2007). Similar 
findings have been reported in comparable 
longitudinal studies from Minnesota (John -
son, Hicks, McGue, & Iacono, 2007), Ger -
many (Lüdtke, Roberts, Trautwein, & Nagy, 
2011), Finland (Josefsson et al., 2013), and 
Italy (Vecchione, Alessandri, Barbaranelli, 
& Caprara, 2012).
Since 2008, researchers have paid a tre -
mendous amount of attention to personality 
trait development in adolescence. The ear -
lier perspectives viewed adolescence as an 
oddly quiescent period of the life course in 
which there were few, if any, strong increas -
es or decreases in personality traits (Young 
& Mroczek, 2003). More recent work has 
pointed to the possibility of a post-  middle 
school dip in personality, such that most 
adolescents decrease on most of the Big 
Five dimensions from age 10 to ages 12 or 
13, then rebound somewhat (Soto & Tack -
ett, 2015). Moreover, multimethod studies 
have shown that parent ratings of agreeable -
ness and neuroticism declined notably from 
ages 11 to 15 (Göllner et al., 2017). Finally, 
other studies have shown that various fac -
ets underlying the Big Five, such as sensa -
tion seeking and impulsivity, show conflict -
ing patterns of change that may cancel each 
other out at the global level of a trait such as 
conscientiousness (Harden & Tucker-  Drob, 
2011). The data are far from definitive; it 
still appears that adolescence is a uniquely 
quiet time for normative increases or de -
creases in broad personality traits, but the 
lack of normative trends may hide more 
complex changes.
Overall, the findings for patterns of mean-
level change described in 2008 appear to be 
holding up in more recent studies. Child -
hood and adolescence are not periods in 
which systematic changes in traits appear 
to occur. Young adulthood is when most 
trait domains “take off”—traits change 
most during this period of life, and the 
changes are predominantly positive. This 
pattern may change our perspective on what 
is going on in childhood and adolescence: 
Rather than being a key time of personality 
trait development, these ages might be bet -
ter construed as periods of preparation for 
development that comes later, at least in cur -rent Western cultures. In contrast, middle 
and old age are periods of peak consistency 
and fewer systematic changes, but one still 
finds individual differences in personality 
trait change even in this relatively quiet por -
tion of the life course (Hill, Payne, Jackson, 
Stine-  Morrow, & Roberts, 2014; Schwaba 
& Bleidorn, 2018). These individual differ -
ences in change not only reflect the contin -
ued plasticity of personality even in old age 
but also are the main source of data for why 
personality traits might be changing.
Why Do Personality Traits  Change?
The question of why personality traits 
change is intrinsically a question of the exis -
tence and correlates of individual differences 
in personality trait change. Not everyone 
changes in the same direction or to the same 
degree; some people change less than their 
peers, while others change more than the 
norm (De Fruyt et al., 2006; Robins, Fraley, 
Roberts, & Trzesniewski, 2001; Roberts, 
Caspi, & Moffitt, 2001). There is robust 
evidence for the existence of individual- 
level change across the life course, even into 
old age (Mõttus, Johnson, & Deary, 2012; 
Schwaba & Bleidorn, 2018; Steunenberg, 
Twisk, Beekman, Deeg, & Kerkhof, 2005). 
Thus, the possibility of finding correlates 
and therefore potential causes of personality 
trait change exists at all stages of life.
A large volume of research has now 
tracked life events and life experience cor -
relates and personality trait change (Blei -
dorn, Hopwood, & Lucas, 2018). Achieve -
ment- and work-  related experiences have 
been linked to changes in personality traits 
across the life course. For example, children 
who increased their effort on homework 
showed commensurate increases in con -
scientiousness (Göllner et al., 2017); older 
students prepping for a major test showed 
similar increases (Bleidorn, 2012). Achiev -
ing more in work through attaining higher 
status was associated with increases in the 
social dominance facet of extraversion and 
sometimes conscientiousness-  related traits 
(Clausen & Gilens, 1990; Elder, 1969; Le, 
Donnellan, & Conger, 2014; Roberts, 1997; 
Roberts, Caspi, & Moffitt, 2003). Achiev -
ing higher status at work was also associated 
with increases in masculinity and decreases 
in femininity (Kasen, Chen, Sneed, Craw -