Østergaard, T., Lundgren, T., Zettle, R.D., Landrø, N.I., & Haaland, V.Ø. (2020) Psychological Flexibility in Depression Relapse Prevention: Processes of Change and Positive Mental Health in Group-Based ACT for Residual Symptoms. Frontiers in Psychology, 11, 528. DOI: 10.3389/fpsyg.2020.00528