Psychometric evaluation of the simplified Japanese version of the Athens Insomnia Scale: The Fukushima Health Management Survey

We investigated the psychometric properties of the simplified Japanese version of the Athens Insomnia Scale (AIS-SJ) using baseline data from the Fukushima Health Management Survey. Data from 22 878 men and 27 669 women aged 16 years and older were analysed (M-age = 52.9 +/- 18.6). Participants lived in the Fukushima evacuation zone and experienced the Great East Japan Earthquake. The AIS-SJ was used to assess participants' insomnia symptoms, and its validity was examined by administering the Kessler 6-item Psychological Distress Scale (K6) and assessing education, self-rated health and disaster-related experiences. A confirmatory factor analysis revealed that the two-factor model was a better fit than the one-factor model. The AIS-SJ and its subscales had acceptable reliability (Cronbach's alpha, 0.81). Test of measurement invariance confirmed strict invariance across groups for the participants' characteristics of gender and mental illness history, but not for participants' age. AIS-SJ scores exhibited a near-normal distribution (skewness, 0.45; kurtosis, -0.89). There were significant age differences only among women, and gender differences in AIS-SJ scores with small effect sizes. The AIS-SJ scores had weak-to-moderate correlations with mental illness history, bereavement, experiencing the tsunami, experiencing the nuclear power plant incident, housing damage and losing one's job (polyserial correlations, 0.36, 0.17, 0.13, 0.18, 0.13, and 0.15, respectively), and strong correlations with self-rated health (polyserial correlation, 0.51), psychological distress (r(s), 0.60) and post-traumatic stress disorder (r(s), 0.60). The AIS-SJ is a useful instrument for assessing community dwellers' insomnia symptoms.