An Exploratory Brief Head-To-Head Non-Inferiority Comparison of an Internet-Based and a Telephone-Delivered CBT Intervention for Adults with Depression

•ICBT was noninferior to tCBT in reducing depression after 5 weeks of treatment•There were no differences in dropout rates between iCBT and tCBT•Severe baseline depression was associated with higher week 5 symptom severity Telephone-administered psychotherapy (tCBT) and internet-based treatments (iCBT) may overcome barriers to mental health treatment. TCBT has demonstrated efficacy similar to traditional psychotherapy, however, few studies have compared iCBT to efficacious interventions. This exploratory study examined the noninferiority of iCBT relative to tCBT. We also explored pretreatment moderators of outcome and assessed treatment dropout. As a secondary exploratory analysis of a 304-participant randomized noninferiority trial, we compared iCBT, the first level of a stepped-care intervention, with tCBT on depression outcome after 5 weeks of treatment (prior to stepping). Multiple linear regression models were fit to examine moderators of 5-week depression. Differences in dropout were examined using Kaplan-Meier survival analysis. After 5 weeks of treatment, both interventions significantly reduced depression severity. The effect size difference between the two interventions was d=0.004 [90% CI=-0.19 to 0.19]; the CI did not cross the non-inferiority margin. Pretreatment depression was significantly associated with depression at week 5. The relationship between cognitive strategy usefulness and depression at week 5 differed between interventions, controlling for pretreatment depression. There was no significant difference in dropout between interventions. Given the stepped-care trial design, iCBT and tCBT could not be compared at the end of treatment or follow-up. Analyses were exploratory and should be interpreted with caution. A large sample, powered for noninferiority, found iCBT no less efficacious than tCBT at reducing depression symptoms after five weeks of treatment.