 14. Personality in Young Adulthood  323
ness to experience, agreeableness, and con -
scientiousness, which represent an optimal 
balance between conceptual breadth, de -
scriptive fidelity, and generalizability across 
samples and measures (John, Chapter 2, 
this volume).
We begin by reviewing the literature on 
personality trait stability and change in 
young adulthood. We next discuss findings 
from longitudinal studies that have investi -
gated whether and to what degree person -
ality traits change in response to major life 
transitions in the domains of love and work. 
Specifically, we focus on studies that have 
examined either of three life transitions 
that normatively occur during the period 
of young adulthood: the first romantic re -
lationship, graduation from school/college, 
and parenthood. Before reviewing these 
studies, we first define life transitions and 
propose a general model to explain why and 
how these life events may impact personal -
ity traits. We conclude by outlining impor -
tant areas for future research on personality 
change in young adulthood.
Personality Trait Stability and Change 
in Young Adulthood
Most studies on personality development 
have focused in two indices of change: rank-
order stability and mean-level change (for 
reviews, see Bleidorn & Hopwood, 2019; 
Roberts & Nickel, Chapter 11, this volume; 
Specht et al., 2014). Rank-order stability  re-
fers to the relative ordering of individuals in 
a population over time, commonly quanti -
fied as a test–  retest correlation ( r) across two 
assessment waves. One robust finding to 
emerge from this literature is that the rank-
order stability of personality traits increases 
during young adulthood. Specifically, meta- 
analytic findings suggest that the rank-order 
stability of personality traits increases from 
r = .51 at age 18 to r = .62 at age 39 (Roberts 
& DelVecchio, 2000). These results seem to 
hold for men and women, and across differ -
ent assessment methods and trait domains. 
More recent large-scale longitudinal stud -
ies and meta-  analyses have replicated this 
finding across different samples, measures, 
and cohorts (Briley & Tucker-  Drob, 2014; 
Ferguson, 2010; Lucas & Donnellan, 2011; Specht, Egloff, & Schmuckle, 2011). The 
increase in rank-order stability has at least 
two important implications for personality 
development theories. First, the rank-order 
stability of all Big Five traits is far from 
perfect, implying that personality traits are 
generally open to rank-order change during 
young adulthood. Second, the overall trend 
toward more stability is consistent with the 
increasing influence of stabilizing environ -
ments on personality traits (e.g., stable so -
cial roles, stable living environments) over 
the course of young adulthood (Briley & 
Tucker-  Drob, 2014).
Mean-level change  reflects the degree to 
which a population decreases or increases 
in a personality trait over a specific period, 
typically quantified as a standardized mean 
difference between two time points (e.g., 
Cohen’s d). Numerous longitudinal stud -
ies have investigated the degree and shape 
of personality mean-level changes in young 
adulthood. These studies converge on the 
finding that young adults experience sub -
stantial normative gains in those Big Five 
domains that mark greater social maturity. 
Specifically, the average young adult shows 
increases in emotional stability, conscien -
tiousness, and agreeableness (Roberts et al., 
2006). These mean-level trends generalize 
across cohorts, genders, and, to some ex -
tent, different cultures (Bleidorn et al., 2013; 
Roberts & Nickel, Chapter 11, this volume; 
Wortman, Lucas, & Donnellan, 2012). Al -
luding to young adults’ seemingly increasing 
capacity to become productive contributors 
to society, this pattern has been labeled the 
maturity principle  of personality develop -
ment (Roberts & Mroczek, 2008).
Less consistent results have been reported 
for mean-level changes in openness to ex -
perience and extraversion. Depending on 
the study, these traits have been found to 
increase (Neyer & Lehnart, 2007; Roberts, 
Walton, & Viechtbauer, 2006; Schwaba, 
Robins, Grijalva, & Bleidorn, 2019), or de -
crease (Wortman et al., 2012), or show little 
or no change across young adulthood (Lucas 
& Donnellan, 2011; Schwaba, Luhmann, 
Denissen, Chung, & Bleidorn, 2018; Specht 
et al., 2011). One potential explanation for 
this mixed pattern of results is that different 
facets of extraversion and openness show 
distinct developmental patterns. Supporting 