Cross-cultural validation of the work functioning impairment scale (WFun) among Japanese, English, and Chinese versions using Rasch analysis

Objectives The work functioning impairment scale (WFun) was developed to measure the degree of work functioning impairment in Japanese workers based on the Rasch model. Given that the number of foreign workers employed in Japan and abroad has increased in recent years, a multilingual questionnaire is becoming increasingly necessary to investigate work functioning impairment in these workers. The purpose of this study was to verify the cross-cultural validity of WFun between Japanese, Chinese, and English versions. Methods A cross-sectional study was conducted in two stages. First, the Chinese and English versions of WFun were created. Second, an internet survey was conducted among 1000 Japanese, 400 Chinese, and 300 Americans. Estimates and standard errors of an individual's ability and item difficulty were calculated using the Rasch model. Differential item functioning (DIF) and differential test functioning (DTF) were also examined using Rasch model analyses. Results The effect size of DIF for one item in the English version exceeded 0.5 logit, indicating the presence of some DIF. In contrast, the effect sizes of DIF for all other items were below 0.5 logit, indicating that the influence of DIF was negligible. Furthermore, Rasch measurements according to the raw score for each version of WFun showed strong agreement among the three versions, with an intraclass correlation of 0.98 (95% confidence interval: 0.97-0.99), indicating the absence of DTF. Conclusions Our findings indicate that the English, Chinese, and Japanese versions of WFun have good comparability.