Factors associated with differential response to online cognitive behavioural therapy

Patients differ in their response to treatments. There is obvious clinical utility in establishing patient characteristics that are associated with differential treatment responses (i.e. are effect modifiers or moderators of treatment response). Factors that moderate response to cognitive behavioural therapy (CBT) remain unclear. This study investigates whether factors prognostic of general depression outcome generally are also moderators of response to online CBT in a sample of depressed patients recruited through UK general practices. Secondary analysis of a randomised controlled trial, internet-based psychotherapy for depression. A total of 297 patients referred from 55 UK general practices and suffering from depression were randomly allocated to receive either online CBT or waiting list control. Treatment effect was measured by comparing depression score at 4 months between randomization groups. Treatment effect modification was assessed using regression analyses focusing on interactions between treatment effect and putative moderator variables. Pretreatment severity and marital status moderated treatment response. More severe patients, and patients who were separated, widowed, or divorced, benefited most from the intervention. Weak evidence suggested that treatment effectiveness diminished with increasing recent adverse life events. No evidence was found to suggest that educational attainment, age, and history of depression-moderated treatment response. Secondary analyses of trials comparing two or more treatments allow factors that may moderate treatment response to be distinguished from more general prognostic indicators, although caution is needed in interpreting such exploratory analyses.