Study Design and Subject Recruitment
Data were collected from a broader general population targeted in the survey. Firstly, the survey was conducted with the general population aged 20–70 years and residing across 17 major cities and local districts from March to May 2018. In each major city and local district, all participants were recruited using two strata (age and sex) following the guidelines of the 2016 census of Korea. We used a probability-proportional-to-size technique for sample selection to represent a nationwide sample.(Paul S. Levy 2013) As the response rate was expected to be 30%, approximately 4,000 people were contacted over the 17 major cities and local districts. Finally, 1,200 of them agreed to respond to the survey.
The survey data were collected by skilled interviewers of World Research Co. Ltd., professionalized in conducting surveys in Korea, who explained the purpose and details of the questionnaire to the respondents. All recruiters provided informed consent. The research procedures followed the tenets of the Declaration of Helsinki and were approved by the Institutional Review Board of Seoul National University College of Medicine (IRB No: 1804-024-934).
To assess the validity and sensitivity of the SAT-Life among the general population, all the participants answered the questionnaire starting with socio-demographic characteristics including age, sex, marital status, income, educational level, residential area, religion, and employment status.
In addition to SAT-Life, the survey items were formulated on the basis of validated questionnaires including the 12-Item Short Form Survey (SF-12) that assessed respondents’ physical and mental QOL(Kim et al. 2014), Patient Health Questionnaire-9 (PHQ-9)(Santos et al. 2013; Han et al. 2008) for depression, McGill Quality of Life Questionnaire (MQOL)(Shin et al. 2009) for subjective well-being (especially for spiritual and social support), and Satisfaction With Life Scale (SWLS).(Diener et al. 1985) To measure the impact of different aspects of health status on SAT-Life, we also assessed the respondents’ five health statuses from a holistic point of view (physical, mental, social, spiritual, and general health status).(Yun et al. 2016)
SAT-Life is based on the previously validated SAT-SF questionnaire for use among cancer patients to evaluate their self-management health strategies(Yun et al. 2015; Yun et al. 2017), and then modified to assess the general population’s coping strategies to help them overcome life crises and improve their QOL and well-being. The SAT-Life assessment consisted of three strategy sets: 1) core strategies (SAT-C), 2) preparation strategies (SAT-P), and 3) implementation strategies (SAT-I). Each of the three strategy steps contained 10-item tools describing each step in detail and a four-point Likert scale (never, sometimes, quite often, and always).(Likert 1932) SAT-Life scores were on a scale of 0 to 100, and is from 100-point scoring algorithm.(Yun et al. 2018b) Higher SAT-Life scores mean that participants have healthier and more scheduled life habits. In our study, each of the SAT-Life values were categorized into binary groups with cutoff scores of 66.66 out of 100 to identify the psychometric properties within the general population.
Firstly, to test the reliability of the SAT-Life, we estimated Cronbach's α, which is a measure of internal consistency of patient responses. In general, α ≥ 0.70 was considered appropriate for the aggregation of responses into a single score.(Elvén et al. 2018) Secondly, descriptive statistical analysis was conducted for demographic characteristics of respondents. Third, to assess discriminant validity, we analyzed the general population with high competency in the SAT-Life scores (SAT-C, SAT-P, and SAT-I) under the hypothesis that they would perform better in goal practice, health status, and QOL, and show lower depression. We calculated each of SAT-C, SAT-P, and SAT-I strategy differentiation according to the participants’ socio-demographic variables, goal practice level, five health statuses, physical and mental component summary from SF-12, and depression level on PHQ-9 to determine the validity of SAT-Life for use with the general population. To assess associations between them, univariate logistic analysis was performed to produce odds ratios (ORs). Each SAT-Life score, less than or equal to 66.6, was set as a reference point for comparisons between groups with higher SAT-Life scores on SAT-C, SAT-P, and SAT-I.(Fayers et al. 1995)
Finally, to assess concurrent validity, correlation analyses between SAT-Life, MQOL, and SWLS scores in the general population were conducted. All calculated p-values were two-sided with the significance level set at p < 0.05. SAS statistical package version 9.3 (SAS Institute, Cary, NC, 1990) and R 3.5.1 were used for all analyses.