Reliability and validity of a Japanese version of the Cambridge depersonalization scale as a screening instrument for depersonalization disorder

Aims: The Cambridge Depersonalization Scale (CDS) is an instrument that has obtained reliability and validity in some countries for use in detecting depersonalization disorder under clinical conditions, but not yet in Japan under non‐psychiatric conditions. The purposes of this study were to develop a Japanese version of the CDS (J‐CDS) and to examine its reliability and validity as an instrument for screening depersonalization disorder under non‐clinical conditions. Methods: The CDS was translated from English into Japanese and then back‐translated into English by a native English‐speaking American. After making the J‐CDS, we examined its reliability and validity. Questionnaires that were composed of J‐CDS, the Dissociative Experience Scale (DES), the Zung self‐rating scale and the Maudsley Obsessional–Compulsive Inventory were administrated to 59 participants (12 patients with depersonalization disorder, 11 individuals who had recovered from depersonalization and 36 healthy controls). Results: Cronbach's alpha and split‐half reliability were 0.94 and 0.93, respectively. The J‐CDS score in the depersonalization group was significantly higher than in the healthy control group. The J‐CDS score was significantly correlated with scores of total DES, and DES‐depersonalization. The best compromise between the true positive and false negative rate was at a cut‐off point of 60, yielding a sensitivity of 1.00 and a specificity of 0.96. Conclusions: In this study, J‐CDS showed good reliability and validity. The best cut‐off point, when we use this for distinguishing individuals with depersonalization disorder from individuals without psychiatric disorders, is 60 points.