Testing causal mechanisms of transdiagnostic dissociation in 16-to-25-year-olds: A randomised multiple baseline experimental design series using brief targeted CBT.

Dissociation is a transdiagnostic process implicated in anxiety, depression, and psychosis, yet causal evidence for its psychological mechanisms remains scarce, particularly in youth. We conducted a series of three multiple baseline single case experimental design (SCED) studies with nine NHS patients (aged 16 to 23), each testing a hypothesised mechanism of change: cognitive appraisals of dissociation, perseverative thinking, and affect intolerance. Each participant received four sessions of individual CBT targeting one hypothesised mechanism. Results indicated successful targeting of cognitive appraisals, and partial success for affect intolerance and perseverative thinking. Findings support cognitive appraisals – and tentatively, affect intolerance – as causal mechanisms in youth dissociation. Any causal effect of perseverative thinking was better accounted for by reduced cognitive appraisals in this SCED study. Although phase instability limited inference, this series offers novel causal insights into transdiagnostic dissociation and informs early-stage treatment development for this presentation in youth.