Psychometric analysis of the Swedish panic disorder severity scale and its self-report version

Panic disorder, with or without agoraphobia (PDA or PD, respectively), is a major public health problem. After having established a PD diagnosis based on the DSM or the ICD systems, the Panic Disorder Severity Scale (PDSS) is the most widely used interview-based instrument for assessing disorder severity. There is also a self-report version of the instrument (PDSS-SR); both exist in a Swedish translation but their psychometric properties remain untested.

We studied 221 patients with PD/PDA recruited to a randomized controlled preference trial of cognitive-behavioral and brief panic-focused psychodynamic psychotherapy. In addition to PDSS and PDSS-SR the participants completed self-reports including the Clinical Outcome in Routine Evaluation - Outcome Measure, Montgomery Åsberg Depression Rating Scale, Sheehan Disability Scale, Bodily Sensations Questionnaire and the Mobility Inventory for Agoraphobia.

PDSS and PDSS-SR possessed excellent psychometric properties (internal consistency, test-retest reliability) and convergent validity. A single factor structure for both versions was not confirmed. In terms of clinical utility, the PDSS had very high inter-rater reliability and correspondence with PD assessed via structured diagnostic interview. Both versions were sensitive to the effects of PD-focused treatment, although subjects scored systematically lower on the self-report version.

The study confirmed the reliability and validity of the Swedish versions of PDSS and PDSS-SR. Both versions were highly sensitive to the effects of two PD-focused treatments and can be used both in clinical and research settings. However, further investigation of the factor structures of both the PDSS and PDSS-SR is warranted.

ClinicalTrials.gov identifier: NCT01606592.