Early changes, attrition, and dose–response in low intensity psychological interventions

Objectives
To investigate if early symptom changes in brief low intensity psychological interventions (guided self-help and psycho-education using cognitive behavioural therapy principles) are predictive of final treatment outcome.

Design
Retrospective cohort data analysis.

Method
Clinical records for 1,850 patients who screened positive for depression and/or an anxiety disorder were analysed. Reliable and clinically significant improvement (RCSI) on depression (Patient Health Questionnaire-9: PHQ-9) or anxiety (generalized anxiety disorder-7: GAD-7) outcome measures after treatment was the primary outcome. Change scores ≥6 on PHQ-9 and ≥5 on GAD-7 were taken as indicative of reliable improvement (RI). The model assumed that RI in the earliest treatment sessions would be predictive of RCSI post-treatment. Predictive accuracy was assessed by calculating the area under the curve (AUC), as well as positive and negative predictive values. Diagnostic odds ratios were also estimated, adjusting for confounders such as baseline severity, use of medication, and pre-treatment symptom change.

Results
The AUC estimates for session-to-session change scores ranged between .62 and .88, indicative of modest to high predictive reliability. Predictive accuracy was higher for patients who had four or more treatment sessions, with more than 70% of patients with RCSI being accurately identified as early as sessions 1–3. Attrition rates were significantly associated with poor outcomes. Results suggest that at least four therapy sessions are necessary to achieve more than 50% RCSI rates, and the dose–response effect appears to decline in treatments longer than six sessions.

Conclusions
Patients showing RI early in treatment were at least twice as likely to fully recover compared to those without early RI.

Practitioner points

Patients showing early response to low intensity therapy are at least twice as likely to recover at the end of treatment.
Dropout from treatment is associated with poor clinical outcomes.
Optimal recovery rates were observed for treatments with a total length of between four and six sessions; the dose–response declined in lengthier treatments.
Randomization to different treatment lengths is necessary to confirm this dose–response effect with greater certainty.