The main objective of this study was to test the psychometric properties of the Polish version of SDQ-20 and the capacity of this instrument, alongside a set of five questions derived from it (SDQ-5), to screen for dissociative disorders. The Somatoform Dissociation Questionnaire (SDQ-20) has been used in many language versions to evaluate the severity of somatoform dissociative symptoms, but no such tool has existed in Polish.

Both pen-and-paper (p&p) and online versions of SDQ-20 were tested. Validity and reliability were examined in a sample of 597 participants in non-clinical (n=323) and clinical (n=274) groups, who completed the tests p&p (n=79) or online (n=518). The mixed-clinical group included 20 patients diagnosed with dissociative (conversion) disorders using TADS-I, and people with other disorders.

The Exploratory Factor Analysis with Principal Component Analysis method of parameter estimation without rotation confirmed unidimensionality of p&p and online versions of SDQ-20. Psychometric properties of the original SDQ-5 were unsatisfactory. Subsequently, an alternative version (PSDQ-5) with a different set of questions derived from SDQ-20 was examined. Reliability of both versions was corroborated by a Cronbach's alpha coefficient (SDQ-20>0.84, PSDQ-5>0.74). The cut-off score maximising sensitivity and specificity was 29.5 (SDQ-20) and 7.5 (PSDQ-5) for dissociative (conversion) disorders (SDQ-20: sensitivity of 95.0% and specificity of 75.6%; PSDQ-5: sensitivity of 95.0% and specificity of 65.9%). People with dissociative disorders had significantly (P<0.001) higher scores in SDQ-20 and PSDQ-5 than patients with other disorders and non-clinical participants (criterion validity).

Conclusion SDQ-20, administered p&p or online, proved to be a reliable tool for the screening of dissociative disorders in Poland. An alternative set of five questions (PSDQ-5) derived from the main instrument also presented good psychometric properties.