Psychometric Validation of a Short-Form Spanish Low Vision Quality of Life Questionnaire (SF-SLVQOL) Using Rasch Analysis: From 25 to 6 Items

Abstract

Introduction The Spanish Low Vision Quality of Life Questionnaire (SLVQOL) assesses vision-related quality of life effectively but requires significant administration time. This study aimed to develop and validate a psychometrically robust short-form version (SF-SLVQOL) using Rasch analysis to reduce respondent burden while maintaining measurement precision in Spanish-speaking populations with visual impairment. Methods Data from the original SLVQOL validation study (n=365; 170 visually impaired, 195 controls) were reanalysed using Partial Credit Model analysis in WINSTEPS. Items were systematically reduced through iterative removal based on point-biserial correlations (<0.4) and misfit statistics (infit/outfit outside 0.7-1.3). The resulting SF-SLVQOL was evaluated for structural validity (unidimensionality, local independence, monotonicity), internal consistency (Cronbach's alpha), criterion validity (correlation with original SLVQOL), construct validity (convergent validity with NEI VFQ-25, known-groups validity across ICD-11 visual impairment categories), differential item functioning by gender and test-retest reliability. Results The 6-item SF-SLVQOL demonstrated excellent unidimensionality (essential unidimensionality=93.6%, variance explained=79.3%), optimal internal consistency (α=1.00) and high criterion validity (r=0.95 with original SLVQOL). Convergent validity with the NEI VFQ-25 was confirmed (r=0.69). Known-groups analysis showed significant discrimination between visual impairment levels (H=132.67, p<0.001). Person reliability (0.91) indicated the ability to distinguish 4.3 performance levels. Test-retest reliability was acceptable (ICC=0.753; 95% CI: 0.569-0.864) with a repeatability limit of 4.89 points. Conclusion: The SF-SLVQOL successfully reduces administration time by 76% while maintaining robust psychometric properties, offering clinicians and researchers an efficient tool for assessing vision-related quality of life in Spanish-speaking populations.