Validating and improving the reliability of the EORTC qlq-c30 using a multidimensional Rasch model.

Objective: The reliability and validity of the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C30) has not been examined while taking into account the correlation between subscales. The reliability of the EORTC QLQ-C30 subscales is modest, thus limiting their utility in both clinical and research settings. The purpose of this study was to validate the factor structure of multiple-item subscales of the EORTC QLQ-C30 and to improve their reliability by means of an item response analysis by using the multidimensional partial credit model.
Methods: A total of 2295 patients with complete data were used for the analysis. One- and nine-dimensional partial credit models were used to fit the data to validate the construct validity of the multiple-item subscales of the QLQ-C30.
Results: The model comparison showed that the nine-dimensional factor structure of multiple-item subscales was satisfactory. The multidimensional partial credit model fit data of the multiple-item subscales of the QLQ-C30 reasonably well. The estimated test reliabilities of each domain obtained from the multidimensional approach were higher than those obtained from the unidimensional approach.
Conclusions: The constructs represented by the multiple-item subscales of the QLQ-C30 were validated. The improved reliability of the multiple-item subscales of the QLQ-C30 under the multidimensional approach can facilitate their applications in clinical and research settings.
(Copyright © 2013 International Society for Pharmacoeconomics and Outcomes Research (ISPOR). Published by Elsevier Inc. All rights reserved.)