292 III. DEvELOPMENT
Rank‑Order Stability of  Personality  Traits
As noted previously, rank-order stability  
refers to the degree to which the relative 
ordering of individuals on a given trait is 
maintained over time. Rank-order stability 
is typically indexed by correlations between 
scores on the same measure across two 
points in time, but in childhood, different 
measures are sometimes used at different 
time points because of the ways that chil -
dren’s traits manifest differently over time. 
Children’s temperament and personality 
traits exhibit some rank-order stability even 
very early in life, and this stability increases 
over time. Roberts and DelVecchio’s (2000) 
meta-  analysis of rank-order trait stability 
obtained these population cross-time corre -
lations for traits in childhood: 0 to 2 years = 
.35; 3 years to 5 years = .52; and 6 years to 
11 years = .45. Later studies have suggested 
that rank-order stability may be even higher 
in childhood, when the results are corrected 
for measurement error (Ferguson, 2010) and 
when stronger measures are used (De Fruyt 
et al., 2008; de Haan, De Pauw, Van den 
Akker, Dekovic, & Prinzie, 2017; Prinzie 
& Dekovic, 2008). Laboratory assessments 
of traits likewise show moderate to strong 
stability for youth’s observed behavioral ten -
dencies (reviewed in Shiner, 2014), although 
the stabilities are somewhat lower than those 
obtained using questionnaire measures (e.g., 
Dyson et al., 2015). Far from being transi -
tory, children’s and adolescents’ traits are 
an important, enduring aspect of their indi -
viduality across childhood and adolescence, 
although change certainly does occur.
Mean‑Level Change in  Personality  Traits
Mean-level changes  involve changes in the 
average levels of traits across different peri -
ods of the life course. Given the rapid bio -
logical, cognitive, emotional, and environ -
mental changes that take place during the 
first two decades of life, it seems plausible 
that children and adolescents would show 
significant mean-level change in personality 
traits. The literature on mean-level changes 
in early and middle childhood is relatively 
limited but does point to some intriguing 
patterns of mean-level change in childhood 
and the transition to adolescence.Early in childhood, children change rap -
idly, which results in significant mean-level 
changes as new capacities come online. In -
fants begin to express the primary emotions 
of joy, surprise, fear, sadness, and interest 
within the first year of life (Lewis, 2000), 
which suggests that mean levels of indi -
vidual differences in those emotions should 
increase over time. Infants develop stronger 
tendencies to smile, vocalize, and laugh dur -
ing the first year (Bates, Schermerhorn, & 
Goodnight, 2010). The biological fear sys -
tem comes online in the latter part of the 
first year (Rothbart, 2011), which suggests 
that individual differences in fear and inhi -
bition should increase during this first year. 
Mean levels of anger gradually increase over 
the first several years (Deater-  Deckard & 
Wang, 2012), as do empathy and prosocial 
behavior (Knafo & Israel, 2012). Physical 
aggression likewise increases from infancy 
onward and peaks around age 3 (Tremblay 
& Nagin, 2005). The more self-  regulatory 
aspects of temperament, specifically, atten -
tion and effortful control, develop rapidly in 
early childhood as well, as several attentional 
systems come online during the latter part of 
the first year (Rueda, 2012). Thus, as traits 
become better established aspects of chil -
dren’s individuality in the first years of life, 
mean levels of emotion-  focused and regula -
tory traits—  including extraversion, activity 
level, negative emotionality, self-  control and 
attention, and empathy/altruism—  increase 
overall during early childhood.
In the preschool years and middle child -
hood, several patterns of mean-level change 
emerge. Extraversion tends to decrease in a 
linear fashion over this time (De Fruyt et al., 
2008; Prinzie & Dekovic, 2008; Soto, 2016; 
Van den Akker, Dekovic, Asscher, & Prinzie, 
2014); early on, this may occur because of 
decreases in energy and optimism, but later 
in childhood, this may include drops in ex -
pressiveness as well (de Haan et al., 2017). 
For neuroticism, in parent reports, the more 
internalizing aspects increase in early child -
hood (e.g., self-  confidence goes down and 
anxiety goes up) (de Haan et al., 2017) and 
in middle childhood (Prinzie & Dekovic, 
2008; Soto, 2016). This may occur because 
of children’s growing abilities to reflect on 
themselves and to consider themselves in 
comparison to others, as reviewed earlier. 