Young and Middle Adulthood 27qualities may depend less on personality similarity than on other factors such as
goal facilitation and reciprocal support (Montoya & Horton, 2013; Neyer & Lang,
2003; Neyer et al., 2011). Such discrepancies between perceived and actual similar-
ity in different personality characteristics regarding liking and closeness in friend-
ships call for further examination of the underlying processes.
In sum, especially so- called social traits (extraversion, agreeableness; Denissen &
Penke, 2008) and related characteristics (self- esteem, narcissism) reliably predict
the formation and quality of friendships. This is not surprising given that these
characteristics describe how people deal with each other: outgoing, dominant
(extraversion), cooperative, friendly (agreeableness). Further efforts are needed to
understand the divergent effects of perceived and actual similarity in various per-
sonality characteristics on friendship quality. Here, dyadic or round- robin study
designs (Kenny, 1994) are necessary, because friendship and similarity of per-
sonality characteristics are phenomena that concern two (or more) people. These
study designs enable researchers to examine how characteristics of one friend and
the interaction between friends influence friendship quality (Back, Baumert et al.,
2011). In addition, such studies should follow friends over time (i.e., short- term
longitudinal studies), as friendships take time to develop. Next, we review the cur-
rent knowledge on longitudinal friendship development, which, however, often
neglects the dyadic aspects.
Friendship Development
Adolescents and young adults have the largest friendship networks and place the
greatest emphasis on friendships compared with people at earlier and later periods
in life (Hartup & Stevens, 1997; Wrzus, Hänel, Wagner, & Neyer, 2013). Next, we
detail how friendships develop both normatively and related to life transitions dur-
ing young and middle adulthood. We focus on changes in the number of friendships
and then address qualitative changes.
Changes in the Number of Friendships
Socioemotional selectivity theory states that young adults are more strongly moti-
vated to gather knowledge and information, as their remaining lifetime often seems
infinite (Carstensen, 1995). Information acquisition is best achieved from diverse
sources, such as a large number of friends. A recent meta- analysis confirmed that
during young adulthood people continue to accumulate friends, hence their friend-
ship networks increase (Wrzus et al., 2013). Figure 2.1 depicts the observed longi-
tudinal changes in friendship networks, personal networks (mainly family members
and friends), and global networks (various kinds of social relationships, e.g., with
family, friends, coworkers, acquaintances, etc.). Studies with young adults (mean