Forward translation and back translation
In creating the Japanese version of the SOMS, we first obtained the necessary permission from Prof. Pearlin. Second, our colleagues conducted a forward translation. Third, a bilingual person performed a back translation. Finally, Pearlin checked the back-translated items, and the items were revised based on his comments.
This survey targeted 4,000 men and women aged 25–74 living in Japan as of January 1, 2014, categorized them according to the region and size of the city in which they lived, randomly extracted 200 municipalities, and randomly extracted individuals after categorizing for sex and age based on the resident registries of each municipality. This method was thereby a stratified two-stage extraction method. During the period from February to March 2014, in which self-administered questionnaires were sent out, 2,067 responses were collected using a leaving method (response rate 51.7%). Cases with inadequate answers about the SOMS were extracted. The final sample size was 954 male and 1,101 female respondents, with a mean age (SD) of 50.0 (14.2). This research was approved by the institutional review board of The Open University of Japan.
Sense of mastery scale
The SOMS version used was Pearlin and Schooler’s 7-item version. This version included statements such as “There is really no way I can solve some of the problems I have” and “Sometimes I feel that I’m pushed around in life”, and used a 4-point Likert scale with possible responses of “strongly disagree”, “somewhat disagree”, “somewhat agree”, and “strongly agree” (Pearlin and Schooler 1978).
Sense of coherence
The sense of coherence (SOC) refers to the sense of looking at or confronting one’s life and environments with the ability to cope with stressors. A 13-item SOC Scale (SOC-13) was used. The reliability and validity of this scale has been demonstrated (Eriksson and Lindström 2005). The total score was tallied using a 7-point semantic differential to serve as the SOC score. Cronbach’s alpha coefficient = .84
Mental health inventory
Mental health was measured using the Japanese version of the five-item Mental Health Inventory (MHI5) related to depression and anxiety from the Medical Outcome Study Short Form (Rumpf et al. 2001). The reliability and criterion-related validity of this scale were verified for the Japanese population aged 16 or older (Yamazaki et al. 2005).
Self-rated health (SRH) was measured on a 5-point scale ranging from “poor” to “excellent” in response to questions such as, “How is your present health?” SRH has been shown to affect survival rates controlled for objective health status (Idler and Benyamini 1997).
Life satisfaction was measured with a 5-point scale with the responses, “unsatisfactory”, “rather unsatisfactory”, “neither unsatisfactory nor satisfactory”, “rather satisfactory”, and “satisfactory” in response to questions such as, “How is the entirety of your life?”
Two versions of the SOMS have been used in previous research, a 7-item version (SOMS-7) and a 5-item version (SOMS-5) that excludes two reverse items from SOMS-7. In recent years, SOMS-5 has been used frequently because of its good reliability (Deeg and Huisman 2010). In this study, both versions were weighed. First, reliability analyses [Cronbach’s Alpha coefficients (Alpha)] and item-total correlations were computed. Second, confirmatory factor analysis by structural equation modeling was performed to examine factor validity. Third, sex and age group differences were examined using Student’s t test and one-way ANOVA. Finally, partial correlation analysis, controlled for age and sex, was performed to examine the relationships between the SOMS and related factors including SOC, MHI5, SRH and life satisfaction, as the construct validity. All analyses were conducted using IBM SPSS Statistics 22.0.