Evaluation Study of Medical-Social Collaboration Model for Middle-aged and Older Adults With Depressive Symptoms

The goal of this clinical trial is to learn if a medical-social collaboration model works to reduce depressive symptoms in middle-aged and older adults with subsyndromal depressive symptoms who are waiting for their first psychiatric appointment. Secondary outcomes of the study include reduced anxiety symptoms, reduced loneliness, reduced rumination, reduced self-criticism, improved self-reassurance, improved resilience, improved self-efficacy, improved health-related quality of life, as well as improved quality-adjusted life years, and reduced healthcare service utilisation. Researchers will compare a medical-social collaboration model to a self-management booklet. Participants will: * Receive CBT-based stepped-care interventions through the medical-social collaboration model or a self-management booklet. * Complete a survey about their mental health and service use every three months until their first psychiatric appointment.