Item analysis of the gastroesophageal reflux disease quality of life instrument QLICD-GERD based on classical test theory and item response theory

Gastroesophageal reflux disease (GERD) is a common digestive disorder that severely affects patients’ physical and psychological health, leading to a substantial decline in health-related quality of life (HRQoL). The Quality of Life Instrument for Chronic Diseases–Gastroesophageal Reflux Disease (QLICD-GERD, V1.0) was developed to comprehensively assess the impact of GERD using both generic and disease-specific modules. This study aimed to analyze the psychometric properties and item performance of the QLICD-GERD (V1.0) using both Classical Test Theory (CTT) and Item Response Theory (IRT), in order to provide theoretical and empirical support for its further refinement. A total of 207 patients with gastroesophageal reflux disease (GERD) were recruited from the Department of Gastroenterology of a tertiary hospital in Yunnan Province, China, between January 2022 and December 2024. A total of 207 patients with GERD from the Department of Gastroenterology of a tertiary hospital in Yunnan Province (January 2022–December 2024) were investigated using the self-administered QLICD-GERD (V1.0). CTT methods—including Cronbach’s alpha, split-half reliability, standard deviation (SD) analysis, correlation analysis, and factor analysis—were applied to evaluate reliability and validity. IRT was used to estimate item discrimination (a), difficulty parameters (b1–b4), and average information (I), using the Samejima graded response model. SPSS 27.0, AMOS, and Multilog 7.03 were used for data analysis. In CTT analysis, 42 out of 48 items met the criteria of at least three statistical methods and were rated as good, while six items were rated as poor. The overall Cronbach’s alpha of the scale was 0.848, and the split-half reliability was 0.905, indicating satisfactory internal consistency. The KMO value was 0.755, with a cumulative variance contribution of 68.51%. The revised confirmatory factor analysis (CFA) model achieved improved fit indices (χ²/df = 2.493, RMSEA = 0.084, GFI = 0.700, CFI = 0.691, TLI = 0.666, IFI = 0.697). Under IRT analysis, item discrimination ranged from 0.89 to 1.44, and most difficulty parameters increased monotonically with grade levels (B1→B4). Average information values ranged from 0.064 to 0.529: 9 items in the physical domain, 2 in social, 1 in spiritual, and 14 in the disease-specific domain were classified as poor, 20 good, and 2 excellent. The QLICD-GERD (V1.0) demonstrates overall good psychometric properties, with strong reliability, validity, and discrimination. The psychological and social domains performed best, while several items in the physical and spiritual domains require refinement to improve measurement precision. The combination of CTT and IRT provides a comprehensive framework for optimizing the instrument’s structure and enhancing its clinical applicability for assessing quality of life among GERD patients.