Validity and reliability of the Spanish version of the Somatoform Dissociation Questionnaire (SDQ-20)

Background: The Somatoform Dissociation Questionnaire (SDQ-20) is a self-reported questionnaire measuring somatoform dissociation. The aim of this study is to analyze the psychometric properties of the Spanish version of the SDQ-20 and its short version (SDQ-5). Methods: Validity and reliability were examined in a sample of 360 psychiatric outpatients: 38 dissociative (conversion) disorders, 30 dissociative (psychoform) disorders, and 292 patients suffering from other disorders. Dissociative disorders were diagnosed using the SCID-D and a specific interview for conversion disorders. Results: Subjects meeting criteria for any dissociative or conversion disorder scored significantly higher in the SDQ-20 (criterion validity). Somatoform dissociation, psychoform dissociation and early trauma were significantly correlated (construct validity). An alpha coefficient of .866 (reliability) and a test-retest correlation of 0.91 were obtained. The cut-off score maximizing sensitivity and specificity was 27.5 for psychoform dissociative disorders (sensitivity of 81.6% and specificity of 71.0%) and 29.5 for conversion disorders (81.6% and 71.0%). For the SDQ-5, the coefficient alpha was 0.561 and the selected cut-off score was 5.5 (sensitivity of 73.33% and specificity of 70.41%). Conclusions: The Spanish version of the SDQ-20 presents good psychometric properties while the SDQ-5 shows worse characteristics and its use with Spanish samples is not recommended.