Cultural Differences in Responses to VF-14 among Preoperative Cataract Patients: Application of the Generalized Random Coefficients Rasch Model

Previous study, using the VF-14 measure, has shown that cataract patients in the United States report higher levels of visual function than those in Korea. A missing answer is whether this difference resulted from biased items of the VF-14 or a real difference caused by potential cross-cultural factors. This study used the generalized random coefficients Rasch model to assess differential item functioning (DIF) in visual function (measured by VF-14) of preoperative elderly cataract patients in Korea and the United States. The study sample consisted of 132 patients with a mean age of 67 years and an evenly distributed gender.

The results showed that Koreans were less able to perform difficult tasks, e.g., reading small print and reading the newspaper. Koreans however reported less difficulty in performing easy tasks, e.g., recognizing people, watching TV, and reading large print. Only 2 items exhibited DIF: reading the newspaper and recognizing people. Compared with US patients who had the same ability level, Koreans showed more difficulty in reading the newspaper and less difficulty recognizing people. Pooled data fit well in the Rasch model, indicating that the VF-14 was unidimensional and formed hierarchical order of items.

Results suggest that lower overall visual function of Korean patients may be partly explained by biased items caused by cognitive difference in defining visual function and/or mistranslation of VF-14 into Korean. A greater portion of difference in visual function may be real. Despite the existence of DIF, psychometric properties of the VF-14 were sound.