Reductions in the internalising construct following internet-delivered treatment for anxiety and depression in primary care.

Depressive and anxiety disorders are different manifestations of a latent internalising construct. To date, efficacy studies have tended to focus on disorder-specific outcomes, rather than underlying dimensions. This study examined the effect of a transdiagnostic internet-delivered cognitive behavioural therapy (iCBT) on the internalising construct in a primary care sample. Participants included 635 patients aged 18 years or over who were prescribed a six lesson transdiagnostic iCBT program for anxiety and depression by their primary healthcare professional. All patients completed the Patient Health Questionnaire 9, the Generalised Anxiety Disorder 7-Item Scale, the Mini Social Phobia Inventory and the Panic Disorder Severity Self-Report Scale at baseline. 325 of these patients completed the program and provided data on each of these scales during the final lesson. Reductions in the latent internalising construct were assessed within a longitudinal factor analysis framework that compared internalising factor means before and after treatment. The within group mean reduction in the latent internalising construct was large (ES = 1.23, SE = 0.09; p < 0.001). Due to the lack of a control group, between group reductions in the latent internalising construct could not be investigated. This study demonstrated that there are clinically significant reductions in the latent internalising construct following transdiagnostic iCBT for anxiety and depression.