Relationship between outcomes and processes in patients with chronic low back pain plus depressive symptoms: idiographic analyses within a randomized controlled trial.

Objective: This study explored the extent to which within-patient changes in processes targeted in Acceptance and Commitment Therapy (ACT) and Behavioral Activation Therapy for Depression (BATD) are associated with changes within-patient in pain intensity and depressed mood and evaluated the extent that process-outcome relationships differed between patients.

Methods: An idiographic analysis embedded within a randomized controlled trial comparing ACT, BATD, and treatment-as-usual (TAU) was conducted to examine the strength of the relationship between outcomes and process variables in patients with chronic low back pain (CLBP) plus depressive symptoms. Based on data from ecological momentary assessment in patients (n = 82), the level of heterogeneity and the pooled effects of these relationships during the intervention period (70 days) were explored.

Results: Overall, a high level of heterogeneity was identified in the relationship between pain intensity or depressed mood and psychological inflexibility or behavioral activation. Individual differences in the relationships between outcomes and process variables were identified in individual people during the intervention period. These individual differences appear independent of the group (ACT, BATD, and TAU) and other definable differences (responders/non-responders, completers/non-completers, and clinical depression/non-clinical depression).

Conclusions: These findings suggest the potential utility of personalizing psychological interventions according to the therapeutic needs of these patients.