Efficacy and mechanism of change in transdiagnostic CBT for social anxiety using single case experimental design

Abstract

This study examined the effectiveness and mechanism of change (MOC) in a novel transdiagnostic cognitive behaviour therapy (txCBT) for social anxiety disorder (SAD) using a single-case experimental design (SCED) more precisely a non-concurrent multiple baseline. Two participants diagnosed with SAD received txCBT based on Salkovskis ’ theory that the belief change, from the current and most maladaptive belief(s) about patient‘s emotional problems (Theory A) to more adaptive and realistic alternative(s) (Theory B) is a MOC in CBT in general. Symptom severity and cognitive processes were recorded in session and via ecological momentary assessment (EMA) with the m Path (2025) app four times weekly.Visual and statistical analyses, including calculations of Reliable Change Index (RCI), Kendall’s Tau, and Tau-U, indicated significant symptom reductions, particularly in Social Phobia Weekly Summary Scale (SPWSS) and Theory A. Three most distressing thoughts (TMDT) scores showed improvement but were less consistent across participants. Belief in Theory A strongly correlated with symptom change, while Theory B showed weaker associations. provided strong indications that treatment effects generalized beyond the therapy setting. Results support txCBT as an effective intervention for SAD, with belief change in Theory A emerging as a key mechanism of change. These results provide preliminary support for the role of cognitive flexibility as a transdiagnostic process in CBT. Further research with larger samples and extended follow-up periods is needed to confirm these findings.