Validity and reliability of the Thai version of the work functioning impairment scale (Thai WFun)

Background In Thailand's agricultural sector, physically demanding labor and a high prevalence of chronic health conditions present substantial challenges to maintaining work capacity. However, few tools are available to assess work capacity among farmers. Objective This study aimed to evaluate the validity and reliability of the Thai version of the Work Functioning Impairment Scale (Thai WFun). Methods The study involved 385 rice farmers from Prakhon Chai district, Buriram province, Thailand, during November and December 2023. The WFun was translated from Japanese to Thai using a standard translation procedure. Participants then completed questionnaires, including the Thai WFun and the Work Ability Index (WAI). The convergent validity between the Thai WFun and WAI was examined through analysis of variance with linear trend tests. The factorial validity was assessed through confirmatory factor analysis (CFA) based on a one-factor model. The reliability of the Thai WFun was assessed using Cronbach's alpha. Results A significant linear trend was observed, indicating that as WAI scores decreased, Thai WFun scores increased (p < 0.001). Sub-factor analyses revealed similar patterns, including the physical and mental demands of work, a comparison with highest work ability ever, and absenteeism in the past year (all p < 0.001). CFA results demonstrated a reasonable model fit. The scale exhibited moderate internal consistency, with Cronbach's alpha of 0.668. Conclusions The findings validate the Thai WFun as a reliable tool for assessing work capacity among rice farmers, with potential to guide tailored occupational health strategies in agriculture.