More Friends, Better Friends, or Vice Versa? An Exploration of Bidirectional Associations Between Friendship Quantity and Quality from Early to Middle Adolescence.

Friendship is a multifaceted construct, with both friendship quantity and quality empirically linked to adolescents' psychosocial adjustment. Yet, their longitudinal associations remain unclear, particularly in interdependence-oriented cultures. The current study examined the bidirectional associations between friendship quantity and quality using four-wave longitudinal data. Participants were 2,118 Chinese adolescents (47.7% female) followed annually from Grade 6 (M_age = 12.31 years, SD = 0.49) to Grade 9. Participants' perceptions of same-sex best friendship quality were measured via self-report, whereas friendship quantity was operationalized as the given, received, and mutual nominations within the classroom, respectively. Results from random-intercept cross-lagged panel models showed that friendship quantity and quality were positively correlated at the between-person level. At the within-person level, only the prospective effect of friendship quantity on friendship quality was significant. Specifically, the number of given friendships to same‑sex peers uniquely predicted increases in same‑sex best friendship quality. No gender differences were observed in these associations. These findings highlight that adolescents' active friendship choices can facilitate the development of friendship quality from early to middle adolescence.