Participants and procedures
Participants were injured workers who had filed accepted workers’ compensation claims following work-related musculoskeletal injuries in Korea. They were recruited at six Korea Worker’s Compensation & Welfare Service (KCOMWEL) hospital rehabilitation centers. Claimants were eligible if they were: (i) absent from work due to a musculoskeletal injury ranging from a fracture to an amputation sustained at work; (ii) in treatment, such as a sub-acute intensive rehabilitation program, tailored-exercise program, or work hardening program at a KCMWEL hospital; (iii) aged 18–65 at the time of the survey; (iv) without central nervous complications; (v) able to understand and speak Korean.
A face-to-face survey was conducted by the authors and trained social work graduate students between September 2016 and September 2017. Participants were informed about the research study and were asked to consent to participate. Then, they were asked questions regarding demographic information, RTWSE, and other variables. Participants were compensated about $45 for completing the survey. Ultimately, 254 injured workers participated: 202 were under treatment (79.5%); 52 had returned to work after treatment (20.5%).
Translation procedure
A forward-backward procedure was applied to translate the RTWSE-19 from English into Korean. After receiving permission from the corresponding author of the RTWSE-19 scale14 via email, a forward translation was made of the original English-language version of the scale into Korean. Two Korean versions were made separately by a professional translator and a rehabilitative medicine doctor who were bilingual in Korean and English, and the authors of this study unified the two Korean translations after discussion of conceptual equivalence and cultural differences. The Korean scale was reviewed by a PhD candidate in Korean language and literature, and then translated back into English by a professional translator unfamiliar with the original English version. The corresponding author reviewed discrepancies between the back-translated scale and the original English-language scale and confirmed the back-translation version, pointing out minor errors in items 5 and 17. One was that the word “job performance” in the original item 5 (“Could meet expectations for job performance”) was back-translated into “job duties.” The authors intended job performance as a formal written evaluation of employees’ work, and the Korean word for job performance was corrected after discussion. The other was that the back-translated version of the original item 17 (“Could discuss openly with your supervisor things that may contribute to your discomfort”) lacked the word “supervisor”; it was corrected.
Measures
RTWSE was measured using the RTWSE-19, a self-report measure intended to assess workers’ confidence about resuming work after the onset of low-back pain. The scale consists of 19 items and three subscales: meeting job demands (7 items), modifying job tasks (7 items), and communicating needs to others (5 items). The response range is from 1 (not at all confident) to 10 (totally confident). The scale was validated through exploratory factor analysis and had high internal consistency for the overall scale and the three sub-scales. Average scores of the items were computed, and higher scores indicated more confidence about returning to work.
Pain intensity was assessed using one item from the intensity subscale of the Von Korff Pain Scale19. Participants were asked to rate their pain intensity on an 11-point numeric rating scale from 0 (“no pain at all”) to 10 (“worst pain possible”) for current pain and the average amount of pain experienced during the past month, respectively.
Fear-avoidance beliefs were assessed using the Fear-Avoidance Beliefs Questionnaire (FABQ)20, an 11-item scale designed to measure a person’s beliefs about how physical activity and work influence his/her back pain. The scale consists of two sub-scales, the FABQ-P and FAB-W. Each item was answered on a 7-point Likert scale ranging from “strongly disagree” to “strongly agree.” This scale was adapted to evaluate health-related beliefs in patients and workers with upper limb and neck pain in several studies21, 22.
General health was assessed using the Short Form-12 (SF-12), a 12-item version of the SF-3623 to measure physical and mental health. Scores range from 0 to 100, with higher scores indicating better health. Scores were computed using the Quality Metric Health Outcomes Scoring Software.
Depression was measured with the Patient Health Questionnaire (PHQ-9)24 which assesses depressive symptoms and consists of nine items on a 4-point Likert scale.
General self-efficacy was assessed using the General Self-efficacy Scale (GSE)25. The GSE is 10-item scale measuring an individual’s stable sense of personal competence to deal effectively with a variety of stressful situations. Each item was rated from 1 (“not at all true”) to 4 (“exactly true”), yielding total scores between 10 and 40.
Statistical analysis
An exploratory factor analysis (EFA) was conducted to examine the factor structure of the RTWSE-19 scale for the work-related injured worker sample in Korea. EFA was applied because the RTWSE scale had not previously been developed and administered to a Korean sample and because such an analysis was necessary to explore the subscale structure. To determine the number of factors, factor structures were examined for 1–4 factors, and the appropriate factor structure was initially determined by model fit indices and simple loading patterns. If the largest factor loading was below 0.4 or if items were loaded above 0.4 with more than one factor (cross-loaded), items were removed. Goodness-of-fit measures, including the comparative fit index (CFI), Tucker-Lewis index (TLI), root mean square error of approximation (RMSEA), and standardized root mean square residual (SRMR), were used to assess fit. Minimal requirements for adequate model fit were: CFI and TLI values greater than .90 (>0.90: reasonable model fit, >0.95: good model fit), and RMSEA and SRMR values less than .08 (< 0.08: reasonable model fit, < 0.05: good model fit)26. EFA was conducted using maximum likelihood estimation and Quart min oblique rotation to allow for correlation between factors. Missing data were not present in the sample.
Additionally, possible floor and ceiling effects were identified. A floor or ceiling effect is usually defined as more than 15% of respondents achieving the lowest or highest score level, respectively27. The presence of floor or ceiling effects indicates that extreme items are missing in the lower or upper end of the scale, indicating limited content validity. Reliability was analyzed using Cronbach’s alpha to test internal consistency. Pearson’s correlation coefficient was used to evaluate the construct validity of the overall RTWSE scale and its subscales with several validating measures: pain intensity, fear-avoidance beliefs, general health, depression, and general self-efficacy.
MPLUS Version 5.21 (Muthén & Muthén, Los Angeles, CA) was used for the EFA and IBM SPSS Statistics for Windows, Version 21.0 was used for the descriptive statistics.