Both positive mental health and psychopathology should be monitored in psychotherapy: Confirmation for the dual-factor model in acceptance and commitment therapy

- The effects of ACT on depression/anxiety symptoms and positive mental health are only moderately related to each other.
- A large majority of participants improved on either depression/anxiety symptoms or positive mental health, not both.
- Both psychopathology and positive mental health need to systematically evaluated in clinical research and interventions.
- An average treatment effect does not automatically mean that the therapy is effective for all patients and on all outcomes.

The dual-factor model of mental health suggests that enhancing positive mental health and alleviating psychopathology do not automatically go hand-in-hand. This study investigates the relationship between the effectiveness on depression/anxiety symptoms and positive mental health of Acceptance and Commitment Therapy (ACT). It draws on RCT data (n = 250) of a self-help ACT. Patients' depression/anxiety symptoms and positive mental health were completed at baseline, at post-intervention after nine weeks, and at follow-up after five months. Percentage of unique variance of depression/anxiety symptoms explained by positive mental health (and vice versa), and the degree of classificatory agreement between improvements in positive mental health and depression/anxiety, were examined using regression analysis and Reliable Change Index (RCI). Positive mental health, i.e. baseline and change, explained 15% and 12% of the variance in follow-up depression and anxiety symptoms, beyond the 7% and 9% that was explained by baseline levels of depression and anxiety. Depression and anxiety symptoms, i.e., baseline and change, explained 10% and 9% of the variance in follow-up positive mental health, on top of the 35% that was explained by baseline levels of positive mental health. Cross-classification of the Reliable Changes showed that 64% of the participants that improved during the ACT-intervention, improved on either depression symptoms or positive mental health, and 72% of the participants improved on either anxiety symptoms or positive mental health. The findings support the dual-factor model and suggest that it is important to systematically implement measures of both psychopathology and positive mental health in mental health care and therapy evaluations.