Cost-effectiveness of varying degrees and models of therapist-assisted transdiagnostic internet-delivered cognitive behaviour therapy: evidence from a randomized controlled trial

In routine care, Internet-delivered Cognitive Behaviour Therapy (ICBT) is often delivered with therapist support via emails/phone calls, but the cost-effectiveness of varying amounts of therapist support or having therapists specialized in ICBT is not known. This study compared the cost-effectiveness of specialized therapists providing ICBT support once-weekly (1WS) versus providing support once-weekly supplemented with a one-business-day response to patient emails (1W/1BD-S). We further compared the cost-effectiveness of 1W support offered by therapists employed in a specialized clinic (1WS) versus community clinics where therapists primarily deliver face-to-face therapy (1WC). Patients were randomly allocated to groups: 1WS group (n = 216), 1W/1BD-S group (n = 233), and 1WC group (n = 226). At baseline, 12, 24 and 52-week follow-up, patients completed the Treatment Inventory of Costs in Patients with Psychiatric Disorders questionnaire (TiC-P) adapted for use in Canada to assess healthcare use and productivity losses. Additionally, to assess Quality Adjusted Life Years (QALYs) gained, patients completed the EQ-5D-5L at the same time periods. We quantified uncertainties by one-way and probabilistic sensitivity analysis and reported Incremental cost-effectiveness ratios (ICER), cost-effectiveness planes and acceptability curves. Cost-effectiveness over 52 weeks was CAD 3072/QALY for 1WC, CAD 3244/QALY for 1W/1BD-S, and CAD 3528/QALY for 1WS. Our model suggests that 1WS is the best strategy since the incremental cost per QALY is below the $50,000 threshold (ICER is CAD 42,328/QALY compared to the next most effective, 1WC). 1W/1BD-S is dominated by the other strategies. The cost-effectiveness acceptability curves suggest that the 1WS group has a higher probability for cost-effectiveness (38 %) than 1W/1BD-S (30 %) and 1WC (32 %) when the willingness to pay is $50,000 per QALY. These results have important implications for health policymakers deciding on delivery of ICBT for the treatment of anxiety and/depressive disorders.