Young and Middle Adulthood 31friendship gains. Higher levels of openness, in contrast, decreased relationship per-
sistence, thus fostering friendship losses (Zimmermann & Neyer, 2013).
With respect to relationship qualities, higher levels of extraversion accounted
for subsequent increases in friendship importance and closeness with friends,
whereas higher levels of openness predicted decreased contact. Higher levels of self-
esteem promoted decreases of friendship insecurity, while high levels of neuroti-
cism had inverse effects (Neyer & Asendorpf, 2001; Parker, Lüdtke, Trautwein, &
Roberts, 2012). Mund and Neyer (2014) reported a similar pattern of effects for
extraversion and neuroticism on friendship development, and additionally com-
pared personality– relationship transactions across different relationship types (see
Figure 2.2A). As expected, their analyses yielded greater effects of personality on
the development of relationship qualities for friendships than for other relationship
types (i.e., kin, romantic partners, and others). Notably, this study also extended
previous cross- lagged designs by studying effects of earlier personality changes on
subsequent changes in friendship qualities (so- called change- change effects). These
analyses revealed that increases in agreeableness predicted subsequent increases in
contact frequency as well as decreases in conflict. The findings illustrate that per-
sonality characteristics are important predictors to explain individual differences in
friendship development across adulthood.
Friendship Effects on Personality Development
The effects of personality on friendship development are not unidirectional, as close
relationships such as friendships require a certain amount of mutual adaptation
in order to be maintained (Hartup & Stevens, 1997; Reis, Collins, & Berscheid,
2000). Accordingly, friendship experiences also retroact on personality and pro-
mote the dynamic codevelopment of individuals and their relationships. Earlier
research focused on socializing effects of peer groups in childhood and adolescence
(Harris, 1995), whereas recent publications examine the relevance of friendships
for personality trait changes beyond adolescence and during the stages of adult-
hood (Reitz, Zimmermann, Hutteman, Specht, & Neyer, 2014; Wrzus & Neyer,
2016). Accordingly, research on the impact of different forms of living arrangements
revealed that young adults who lived with roommates showed steeper increases in
openness and agreeableness than those who stayed with their parents ( Jonkmann,
Thoemmes, Lüdtke, & Trautwein, 2014).
Effects of relationship fluctuation, that is, the persistence of established relation-
ships and the initiation of new contacts, were substantiated in a study on interna-
tional student exchange (Zimmermann & Neyer, 2013): International relationship
gains of exchange students explained effects of going abroad on the development of
openness and neuroticism. Furthermore, recent research also corroborated effects
of relationship qualities. Best friend support accounted for increases in extraversion
from age 17 to 23 years, whereas higher levels of conflict with best friends were