Linking Friendship Quality Trajectories and Fluctuations to Adolescent Depressive Symptoms: A Four-wave Longitudinal Study.

Adolescence is a period marked by significant changes in friendships; however, while existing research has focused on developmental trajectories of friendship quality, relatively less attention has been paid to fluctuations in friendship quality and their impact on psychological well-being. The present study sought to address this gap by examining whether and how friendship quality trajectories and fluctuations distinctly affect adolescent depressive symptoms. A sample of 1083 seventh-grade Chinese students (39.1% girls; baseline M = 12.91 years, SD = 0.40) from three public junior high schools participated in a four-wave longitudinal study. Results indicated that a declining friendship quality trajectory contributed to increased depressive symptoms, primarily through the mechanisms of reduced self-esteem and heightened insecurity. Beyond the influence of mean initial friendship quality and its trajectory, friendship quality fluctuations also predicted depressive symptoms through reduced self-esteem and heightened insecurity. These findings highlight the critical and distinct roles of friendship quality decline and fluctuations during adolescence, revealing how friendship quality changes shape adolescent depressive symptoms and providing valuable insights for developing targeted interventions to mitigate adolescent depression.