High Social Anxiety in adults is associated with self-report of impaired friendship quality, but not necessarily with impairment reported by friends. Further, prospective prediction of Social Anxiety and friendship quality over time has not been tested among adults. We therefore examined friendship quality and Social Anxiety prospectively in 126 young adults (67 primary participants and 59 friends, aged 17-22 years); the primary participants were screened to be extreme groups to increase power and relevance to clinical samples (i.e., they were recruited based on having very high or very low social interaction anxiety). The prospective relationships between friendship quality and Social Anxiety were then tested using an Actor-Partner Interdependence Model. Friendship quality prospectively predicted Social Anxiety over time within each individual in the friendship, such that higher friendship quality at Time 1 predicted lower Social Anxiety approximately 6 months later at Time 2. Social Anxiety did not predict friendship quality. Although the results support the view that Social Anxiety and friendship quality have an important causal relationship, the results run counter to the assumption that high Social Anxiety causes poor friendship quality. Interventions to increase friendship quality merit further consideration.
