Anxiety Sensitivity as a Mediator of Internet-Based Cognitive Behavioral Therapy for Panic Disorder: A Randomized Controlled Trial with Minimal Therapist Contact
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Background
Internet-based cognitive behavioral therapy (iCBT) is efficacious for panic disorder (PD), yet the mechanisms through which it produces change remain underspecified. Anxiety sensitivity — the dispositional tendency to fear anxiety-related sensations — is theoretically central to the maintenance of PD, but its role as a mediator of iCBT outcomes has not been formally tested in Spanish-speaking populations with minimal-contact delivery formats.
Method
Ninety-five adults meeting DSM-IV-TR criteria for PD were randomized to an 8-week iCBT program ( Free from Anxiety ) with optional email-based therapist support (n = 49) or a waiting-list control (n = 46). Primary outcome was PD severity (PDSS); secondary outcomes included anxiety sensitivity (ASI-3), general anxiety (BAI), and depression (BDI-II). A Baron and Kenny (1986) mediation analysis with bootstrapped confidence intervals (5,000 resamples) examined ASI-3 change as a mediator of treatment effects on PDSS.
Results
The treatment group showed large improvements relative to controls on all outcome measures (PDSS: d = 0.76, 95% CI [0.10, 1.42]; mean d = 1.30 across measures). Mediation analysis confirmed that ASI-3 change partially mediated the treatment effect on PDSS: the indirect effect accounted for 27.4% of the total effect (indirect = 1.85; bootstrap 95% CI [0.36, 3.70]). The direct effect of treatment remained significant after controlling for ASI-3 change ( b = 4.89, p < .001). Full ITT sensitivity analyses confirmed robustness ( d = 0.47–1.47). Gains were maintained at six months ( d = 1.15–1.26).
Conclusions
iCBT for PD reduces anxiety sensitivity as a partial mechanism of change, consistent with cognitive models of panic. These findings extend the evidence base for Free from Anxiety in Spanish clinical populations with high comorbidity and support its viability as a first-step intervention in stepped-care pathways. The anonymized dataset is publicly available at https://doi.org/10.5281/zenodo.20084725 (CC BY 4.0).
