A randomised controlled trial to evaluate the outcomes and mechanisms of a novel digital reasoning intervention for persecutory delusions

Our approach to advancing mental healthcare for people with psychosis is to focus on single symptoms and develop interventions targeting the mechanisms that maintain them. Worries about others intentionally causing harm can range from fleeting paranoid thoughts to more persistent and severe ideas, which are also known as persecutory delusions. A range of biological, psychological and social factors contribute to worries about others causing harm, with the relative contribution varying according to the individual situation. In relation to psychological factors, paranoia is clearly associated with a certain style of reasoning, which can be considered fast thinking (Kahneman, 2011). Fast thinking, includes a tendency to jump to conclusions and belief inflexibility; it is therefore characterised by taking in too little information, high conviction in thoughts, and a lack of consideration of alternative ideas. We will test the clinical efficacy of a new intervention (SlowMo) that targets fast thinking habits in people affected by severe paranoia. SlowMo works by supporting people to slow down for a moment to reduce fast thinking and the subsequent impact of paranoia on their lives. Existing psychological treatments are expensive and hard to deliver: if shown to be effective, SlowMo provides a targeted, inexpensive and practicable intervention. SlowMo has been developed from a user-centred inclusive design approach, to address the challenges to therapy engagement and adherence for people with severe mental health problems. It consists of an easy to use and enjoyable digital interface, thereby harnessing the potential of technology for improving health-related outcomes and reducing costs, in line with the ‘NHS Five Year Forward View’ (Hollis et al, 2015; NHS England, 2014). Thoughts are visualised as bubbles, with different speeds, sizes and colours, to reflect different thinking habits, levels of distress and coping tips. This simple metaphor makes it easier for people to understand thoughts are transient, and that by using coping strategies we can modify them. An interactive digital interface assists the delivery of face-to-face sessions, which are synchronised with a mobile app for use in daily life. A parallel group randomised controlled trial (RCT) with blind assessment in three sites will test whether SlowMo, added to treatment as usual (TAU), reduces severe paranoia more effectively than TAU alone. Participants with distressing severe paranoia and a diagnosis of schizophrenia spectrum psychosis will be randomised 1:1 to the two conditions. SlowMo consists of 8 face-to-face sessions delivered by trained therapists, with the support of an interactive, digital platform that is synchronised to a mobile app for use in daily life. Assessments will be made at baseline, after treatment at 12 weeks, and at 24-week follow-up. The primary outcome is change in paranoia severity over 24 weeks. Secondary outcomes include wellbeing, self-esteem, quality of life, service use, and standard mood and symptom assessments. The sample size of 360 is powered to detect an effect size of 0.4, equivalent to a clinically worthwhile 10-point change on our outcome measure. This calculation takes account of therapist effects, clustering in the intervention arm, and 20% sample attrition. We will examine treatment mechanisms and other sources of treatment-effect heterogeneity: we hypothesise that improvements in a fast thinking (or reasoning) style mediate reductions in paranoia severity and that treatment effects are moderated by working memory, negative symptoms, beliefs about illness and therapy adherence. As well as advancing treatment, evidence of mechanisms and moderators of action will inform theories of paranoia and future stratified medicine approaches. Statistical analyses will be based on the intention-to-treat population. Random effects regression models fitted to repeated outcome measures will estimate treatment effects,