26 Friendship Across the Life Span
showed diverse effects: More agreeable people reported greater friendship inten-
sity (Heyl & Schmitt, 2007; M. A. Johnson, 1989) and less conflict with friends
(Asendorpf & Wilpers, 1998), whereas Neyer and Asendorpf (2001) did not
observe such effects.
Together, the effects of personality traits such as extraversion, narcissism, and
self- esteem on the initial attraction toward new potential friends are fairly well
understood, however, personality effects on the subsequent process of develop-
ing closeness, support, and conflict in friendships need further examination. Other
traits, such as neuroticism, conscientiousness, and openness to new experiences,
might relate to friendships only among specific groups of people or in specific sit-
uations. For example, neuroticism may only be relevant among male friends, for
whom frequent worries and emotional instability are incompatible with traditional
male gender roles. Hence, neuroticism predicted lower status and less influence
only among male friends (Anderson et al., 2001).
Personality Similarity in Friendships
In addition to individuals’ personality traits, the similarity in personality traits of
friends further relates to friendship quality. In general, people state that they pre-
fer others as friends who have similar attitudes, values, and interests (Sprecher &
Regan, 2002). As described before, people usually like similar others because the
similarity suggests that the other person has (similar) positive characteristics, which
make him/ her likable (Montoya & Horton, 2013). Simplified, one could say if peo-
ple think they are good and the other person is similar to them, then the other per-
son also has to be good.
Recent studies on real- life friendship formation showed that perceiving greater
similarity in personality traits predicted friendship formation longitudinally (van
Zalk & Denissen, 2015). However, actual similarity in attitudes, interests, or per-
sonality traits did not predict initial liking or later friendship intensity in real- life
settings (Back, Schmukle et al., 2011; M. A. Johnson, 1989; van Zalk & Denissen,
2015; but see Montoya et al., 2008; Selfhout et al., 2010, for effects of actual person-
ality similarity on friendship selection). Nonetheless, on average, friends are simi-
lar to each other in some personality traits (Selfhout et al., 2010), and even more
similar to each other with respect to sociodemographic characteristics such as age,
education, or socioeconomic status, described as social homogamy (McPherson,
Smith- Lovin, & Cook, 2001; van Zalk & Denissen, 2015).
Similarity in traits, attitudes, or interests among friends may be a byproduct of
social homogamy (e.g., meeting in the neighborhood where people of similar socio-
economic status and political orientation live; McPherson et al., 2001) and fur-
ther environmental factors influencing friendship formations (e.g., meeting during
shared leisure activities that indicate similar interests) instead of a product of active
assortment (Back, Schmukle et al., 2011). Accordingly, liking and other friendship