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 increasingly recognized as a transdiagnostic process implicated in the development and maintenance of anxiety, depression, and psychosis. However, causal evidence for mechanisms underpinning dissociation remains scarce, particularly in youth. Nine NHS patients (aged 16 to 23) participated three multiple baseline single case experimental design (SCED) studies. Every participant received four sessions of individual CBT, with each SCED addressing a different hypothesised mechanism: cognitive appraisals of dissociation, perseverative thinking, and affect intolerance. Results indicated successful targeting of cognitive appraisals, and partial success in targeting perseverative thinking and affect intolerance. They support cognitive appraisals, and partially support affect intolerance, as causal mechanisms in youth transdiagnostic dissociation. Any causal effect of perseverative thinking was better accounted for by reduced cognitive appraisals in this SCED. Across participants, low phase stability of the target measures limited inference, but these findings advance a mechanistic understanding of youth dissociation and inform treatment development.