What moderates digital cognitive behavioural therapy (Sleepio) for insomnia? Findings from a participant-level analysis of 8,549 individuals in 12 randomised controlled trials

Background: Cognitive–behavioural therapy (CBT) is a guideline treatment for several mental disorders and is effective for many patients, but not for all. Despite this evidence base, it has proven more challenging to establish definitive moderators of therapeutic effects with high statistical power. Aims: Our objective was to estimate the effects of a standardised digital CBT (Sleepio) intervention for insomnia among different groups of people, with sufficient power, using personal demographic and clinical characteristics as moderators. Method: A collaborative working group was formed with authors from all 12 published studies of the fully automated (i.e. without therapist support) digital CBT. These studies were identified from a systematic search. Individual participant-level data (IPD) from each study was harmonised from 8549 individuals who had been randomised. We used robust statistical IPD techniques to evaluate moderators. Results: Digital CBT had a large effect for symptoms of insomnia (d = −1.0, 95% CI −1.4 to −0.63). Those with more clinically severe symptoms of insomnia were found to benefit more (d = −1.18, 95% CI −1.34 to −1.01). Individuals who were older, had higher incomes and identified as White achieved greater effects. Participant gender, education and employment status did not moderate insomnia symptoms. Conclusions: Fully automated digital CBT was an effective treatment for insomnia across many different groups of patients. We did not find any reason to withhold digital CBT based on demographic or clinical characteristics of participants. Treatment was somewhat more effective for specific groups of patients.