Validation of DEQ-5 unidimensionality and differential item functioning of Saudi adult populations

Objective: The Dry Eye Questionnaire (DEQ-5) is a questionnaire for dry eyes vital for assessing ocular surface disease severity in dry eye disease (DED). This analysis aimed to comprehensively evaluate its precision, reliability, unidimensionality, and differential item functioning (DIF) irrespective of age and gender. Methods: This cross-sectional research was carried out between March 2021 and March 2022. A systematic random sampling technique selected participants (n=634). The DEQ-5 questionnaire was used in the King Saud University campus clinic and Kingdom Hospital in Riyadh, Saudi Arabia. Statistical analysis was performed using statistical software (SPSS version 28 SPSS Inc., Chicago, IL; for Windows). Standard deviations (SDs), percentages, and averages are used to show the data reliability analysis to test Cronbach's coefficient, which calculated the scale's internal consistency, McDonald's coefficient, and item-rest correlations. Moreover, Rasch Analysis has been performed to check if the DEQ-5 can distinguish different levels of dry eye symptoms. Results: The study revealed that the DEQ-5 performed well in various aspects. At 2, the person separation index (PSI) was satisfactory, indicating good reliability (0.80). Items separation revealed outstanding reliability (1.00), with mean square data for attire and infit within acceptable ranges (0.545-1.674 and 0.578-1.698, respectively). The high-reliability precision (77%) suggests the questionnaire's ability to elicit accurate responses. The analysis confirmed unidimensionality; the first contrast's eigenvalue for unexplained variance is less than 2 (1.79). DIF analysis stratified by age showed that participants aged 16-26 performed better on @3QUESTION than those aged 27-40. Similarly, based on gender, males outperformed females in @1B and @2QUESTION. Furthermore, with a Cronbach's coefficient of 0.767 and a McDonald's coefficient of 0.828, the DEQ-5 demonstrated adequate internal consistency, reaffirming its reliability. Conclusions: The DEQ-5 is a robust instrument for evaluating DED severity, as evidenced by its acceptable precision, reliability, unidimensionality, and DIF analysis results. Understanding its performance across different age and gender groups provides valuable insights for its use in clinical and research settings, ensuring accurate assessment and diagnosis of DED.