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. In a sample of 221 adults with PD/PDA recruited to a randomized controlled preference trial of cognitive-behavioural and brief panic-focused psychodynamic psychotherapy, both forms 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.