Participants
The participants were drawn from registered members of an online survey site, Macromill, Inc [13](Macromill 2020)(Macromill 2020)(Macromill 2020)(Macromill 2020)(Macromill 2020)(Macromill 2020)(Macromill 2020). The company had access to over 2,300,000 potential participants representing all prefectures in Japan and recruited participants based on their demographic attributes to obtain a relatively representative sample. Of the available respondents, a stratified random sample of 1,030 participants completed a web-based questionnaire in order of arrival to the form. Participants were sampled from two strata equally (50% vs. 50%) according to their history of major depressive episodes (MDE), as evaluated by the Mini International Neuropsychiatric Interview (MINI): total scores ≧ 5 or 0 ≦ total scores ≦ 4. Participants had to meet the following criteria to be included in the study: (a) living in Japan and (b) being 20 years of age or older. There were no exclusion criteria. Based on these criteria, the Internet survey company recruited monitors from their potential pool of participants until the targeted number was reached. Participating monitors were awarded approximately 100 tokens (equivalent to 100 Japanese yen) as a reward. Informed consent was obtained from all participants via instructions on the survey. The instructions assured the protection of personal information and explained that any identifying information would be removed from the data.
Assessment instruments
Euthymia scale (ES)
The Japanese version of the ES, the ES-J, was obtained according to the procedure specified in the International Society of Pharmacoeconomics and Outcomes Research (ISPOR) task force guidelines [14]. First, we obtained permission from the original developer of the Euthymia Scale (Professor Giovanni A. Fava) to translate the measure into Japanese [11]. Forward-translation was conducted independently by two Japanese authors (Natsu Sasaki and Daisuke Nishi) and was followed by reconciliation, back-translation, back-translation review, harmonization, and cognitive debriefing. The Japanese version of the 5-item World Health Organization Well-Being Index (WHO-5) was referred to in the latter half of the ES (No.6 to No.10) in forward-translation[15](Inagaki, Ito et al. 2013)(Inagaki, K et al. 2013)(Inagaki, K et al. 2013)(Inagaki, K et al. 2013)(Inagaki, K et al. 2013)(Inagaki, K et al. 2013). The back-translation was conducted by an expert in Japanese and English affiliated with the University of Tokyo who did not know the purpose of the present study. The original developer checked the back-translated measure and confirmed it at the back-translation review. Cognitive debriefing sessions were conducted with six general Japanese people who were recruited using snowball sampling and included graduate students who specialized in mental health, a psychiatrist, and office workers, whose ages ranged from the 20s to 50s. They were asked to complete the harmonized measure and were interviewed about the relevance, comprehensiveness, and comprehensibility of the items. The cognitive debriefing process did not lead to any change in wording. The authors confirmed the cognitive equivalence of the translated ES-J (the scale can be available by contacting the corresponding author).
The original version of the ES-J rating scale is a 10-item self-reported questionnaire. Each item of the ES-J is scored dichotomously as False (0) or True (1), resulting in an overall score ranging from 0 to 10, with higher scores indicating a better euthymic state.
Mini-International Neuropsychiatric Interview (MINI)
The MINI is a widely used clinician-rated scale (i.e., structured interview) for the assessment of axis I psychiatric disorders according to DSM-IV diagnostic criteria [16–19]. Diagnoses are based on dimensional scores (Yes or No) obtained from nine items (e.g., Were you [ever] depressed or down, or felt sad, empty or hopeless most of the day, nearly every day [in lifetime/for the past two weeks]?). History of MDE in lifetime was categorized as Yes (score 5–9) or None (score 0–4). According to the Diagnostic and Statistical Manual of mental disorders (DSM-5), current MDE (endorsed 5–9 items), sub-threshold depression (endorsed 1–4 items), and none (endorsed 0 items) were used as criteria among the total of 9 items [16].
Psychological distress
Psychological distress was evaluated using the Japanese version of the K6 [20, 21]. The K6 is a widely used self-rating scale assessing nonspecific distress during the past 30 days. Each item of the K6 is scored on a Likert scale ranging from never (0) to all of the time (4). The total score of the K6 ranges from 0 to 24, with higher scores indicating more severe psychological distress. A score of more than 13 on the K6 was used to detect severe symptoms of psychological distress. A K6 score of more than 5 was indicative of moderate symptoms of mental distress [22].
The validity of the Japanese version of the K6 was found to be satisfactory [20, 23].
Psychological well-being
Psychological well-being was evaluated using the 42-item version of the Psychological Well-being Scales (PWBS)developed by Carol D. Ryff. The PWBS originally consisted of six subscales, each including seven items, assessing the following six factors: 1) autonomy; 2) environmental mastery; 3) personal growth; 4) positive relations with others; 5) purpose in life; and 6) self-acceptance [24, 25]. Response categories for these items are on a seven-point Likert scale ranging from Strongly disagree (1) to Strongly agree (7). The scores of some items were reversed as recommended in Ryff’s original PWBS [24, 25]. The average scores were calculated for six subscales, with higher mean scores indicating greater psychological well-being. The validity of the Japanese version of PWBS has been recently tested [26].
Resilience
Resilience was evaluated using the Tachikawa Resilience Scale (TRS) [27, 28]. TRS is a 10-item self-administered scale. All items are rated on a 7-point Likert scale, ranging from strongly disagree (1) to strongly agree (7). The total scores ranged from 10 to 70, with higher scores reflecting higher resilience.
The original TRS was in the Japanese language, and several items reflected Japanese culture-bound cognitions. For example, items such as, “I accept things as they are when there are no alternatives” and “I try not to worry about what is beyond my capabilities” can be regarded as culturally appropriate for Japanese individuals because these items reflect the idea of Morita therapy, which guides patients to accept anxiety as it is [28]. The validity of the TRS was acceptable [27].
Life satisfaction
The Satisfaction With Life Scale (SWLS), developed by Diener [29], was used to measure life satisfaction. The SWLS is a 5-item broad-band instrument measuring life satisfaction. Examples of items are, “In most ways, my life is close to my ideal,” and “If I could live my life over, I would change almost nothing.” The SWLS uses a 7-point Likert scale, ranging from strongly disagree (1) to strongly agree (7), yielding a total score ranging from 5 (low life satisfaction) to 35 (high life satisfaction). The validity of SWLS was acceptable [30, 31].
Social support
Social support was assessed using the Japanese short (7-item) version of the self-rated Multidimensional Scale of Perceived Social Support (MSPSS) [32, 33]. It assesses perceived support from each of three sources: family (2 items), friends (3 items), and a significant other (2 items). The items are measured on a 7-point Likert scale ranging from very strongly disagree (1) to very strongly agree (7), with higher scores suggesting greater levels of perceived social support. The mean score of 7 items was used as a total score.
Demographic variables
A questionnaire was administered to assess the following demographic variables: gender (male or female), age, marital status (married, divorced/widowed or single), having a child, household income, and education status (Junior high school, high school, college, undergraduate school, upper than graduate school).
Statistical analyses
Statistical significance was defined as p < 0.05. All the statistical analyses were performed using SPSS 26.0, Japanese version (IBM Inc, Chicago, IL).
Pearson’s correlation coefficients (rs) were calculated to examine the concurrent validity of the ES-J. Positive and moderate to high correlations were expected with rating scales measuring psychological well-being, resilience, life satisfaction, and social support. Negative and moderate to high correlations were expected with measures of psychological distress.
Multivariate regression models and analysis of variance (ANOVA) were conducted to examine the clinimetric sensitivity of the ES-J and test whether this rating scale sensitively distinguishes moderate from severe symptoms of psychological distress and discriminates between patients (i.e., those with past or current history of MDE or with sub-threshold symptoms of depression) and healthy subjects.