Reliability testing of the Persian low-vision quality-of-life questionnaire based on Rasch analysis

Abstract

Objective: Low-vision quality-of-life (LVQOL) questionnaire was recently translated to Persian. Its model fit and construct validity were assessed by exploratory and confirmatory analysis for adults with visual impairment, before. In this study, we aimed to test the reliability of the Persian LVQOL questionnaire based on Rasch analysis. Methods: Overall, 100 low-vision patients and 100 demographic statue-matched control subjects were participated for evaluating reliability aspects. All the participants were asked to complete the Persian LVQOL questionnaire. The low-vision group was asked to fill out the LVQOL 3 months after rehabilitation to determine how rehabilitation changed the quality of life. Rasch analyses of the survey items were conducted using WINSTEPS. Results: All items fitted the Rasch model. Point-measure correlations values varied from .13 to .70, providing a preliminary indication of adequate construct validity. All factor loadings found more than .4. infit values for all other participants were in the acceptable range. All items obtained infit and outfit MSQ values of < 2.0. Patients’ abilities relative to the item difficulty were analyzed. Item difficulty was estimated and item characteristic curves were included. Sufficient unidimensionality, hierarchical order, and equal interval scaring were obtained. Conclusion: The Persian LVQOL questionnaire was reliable enough and it will be valuable in both clinical practice and research.