Two new screening scales for psychological distress, the K6 and K10, have been developed using the item response theory and shown to outperform existing screeners in English. We developed their Japanese versions using the standard back-translaton method and included them in the World Mental Health Survey Japan (WMH-J), which is a psychiatric epidemiologic study conducted in seven communities across Japan with 2436 participants. The WMH-J used the WMH Survey Initiative version of the Composite International Diagnostic Interview (CIDI) to assess the 30-day Diagnostic and Statistical Manual of Mental Disorders--Fourth Edition (DSM-IV). Performance of the two screening scales in detecting DSM-IV mood and anxiety disorders, as assessed by the areas under receiver operating characteristic curves (AUCs), was excellent, with values as high as 0.94 (95% confidence interval = 0.88 to 0.99) for K6 and 0.94 (0.88 to 0.995) for K10. Stratum-specific likelihood ratios (SSLRs), which express screening test characteristics and can be used to produce individual-level predicted probabilities of being a case from screening scale scores and pretest probabilities in other samples, were strikingly similar between the Japanese and the original versions. The Japanese versions of the K6 and K10 thus demonstrated screening performances essentially equivalent to those of the original English versions.

The authors developed the Japanese-language version of the Impact of Event Scale-Revised (IES-R-J) and investigated its reliability and validity in four different groups: workers with lifetime mixed traumatic events, survivors of an arsenic poisoning case, survivors of the Hanshin-Awaji earthquake, and survivors of the Tokyo Metro sarin attack. Evidence includes retest reliability and internal consistency of the IES-R-J. Posttraumatic stress disorder (PTSD) and partial PTSD cases indicated significantly higher scores than non-PTSD cases. The IES-R-J can be a useful self-rating diagnostic instrument particularly for survivors with PTSD symptoms as a clinical concern (PTSD + partial PTSD) by using a 24/25 cutoff in total score. In analysis of scale structure, the majority of intrusion and hyperarousal items were subsumed under the same cluster, whereas avoidance items made up a separate cluster. Female patients indicated higher scores than male patients. A negative weak correlation between age and the score was found only among female earthquake survivors. The IES-R-J can be used as a validated instrument in future international comparative research.

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