The codevelopment of extraversion and friendships: Bonding and behavioral interaction mechanisms in friendship networks.

Empirical evidence suggests that people select friends whose extraversion is similar to their own (selection). However, little is known about whether friends influence extraversion development (influence) and about the interaction mechanisms that underlie friendship selection and influence. We examined whether selection and influence explain similarity in extraversion between friends in two independent samples. Similarity in extraversion predicted a higher likelihood of friendship selection across 4 years in Sample 1 (n = 1,698; Mage = 22.72, SD = 2.99; 49% female) and across a period of 16 weeks in Sample 2 (n = 131; Mage = 21.34, SD = 3.95; 77% female). Friends' extraversion predicted increases in young adults' extraversion in both samples. In Sample 2, we examined the interaction mechanisms underlying selection and influence by combining event-based experience-sampling network changes with diary data on friendship network and extraversion changes. Findings showed that (a) similarity in extraversion predicted positive interaction quality changes and (b) positive interaction quality predicted friendship selection (bonding mechanism). In the same model, (a) friends' extraversion predicted friends' sociable behavior changes, (b) friends' sociable behavior predicted young adults' sociable behavior changes, and (c) young adults' sociable behavior predicted young adults' extraversion changes (behavioral mimicry mechanism). These findings provide unique insight into interaction mechanisms underlying longitudinal links between friendships and extraversion. (PsycInfo Database Record (c) 2020 APA, all rights reserved).