Development and preliminary validation of the chronic obstructive pulmonary disease scale quality of life instruments for chronic diseases-chronic obstructive pulmonary disease based on classical test theory and generalizability theory

Quality of life (QOL) in patients with Chronic obstructive pulmonary disease (COPD) is a major global concern in respiratory care with the specific instruments used rarely being developed using a modular approach. This paper is aimed to develop the COPD scale of the system of QOL Instruments for Chronic Diseases (QLICD-COPD) by the modular approach based on Classical Test Theory and Generalizability Theory (GT). 114 inpatients with COPD were used to provide the data measuring QOL three times before and after treatments. The psychometric properties of the scale were evaluated with respect to validity, reliability and responsiveness employing correlation analysis, factor analyses, multi-trait scaling analysis, and also GT analysis. The Results showed that Multi-trait scaling analysis, correlation and factor analyses confirmed good construct validity and criterion-related validity with almost all correlation coefficients or factor loadings being above 0.40. The internal consistency α and test-retest reliability coefficients (Pearson r and Intra-class correlations ICC) for all domains except for the social domain were larger than 0.70, ranging between 0.70–0.86 with r = 0.85 for the overall. The overall score and scores for physical and the specific domains had statistically significant changes after treatments with moderate effect size SRM (standardized response mean) ranging from 0.32 to 0.44. All G-coefficients and index of dependability were all greater than 0.80 exception of social domain (0.546 and 0.500 respectively), confirming the reliability of the scale further. It concluded that the QLICD-COPD has good validity, reliability, and moderate responsiveness, and can be used as the QOL instrument for patients with COPD.