A New Statistical Approach for Quality of Life Questionnaires in the Assessment of Non-Small-Cell Lung Cancer Cuban Patients

Objectives: To evaluate the dimensionality and item characteristics of the European Organization for the Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ-C30) and the lung cancer module (QLQ-LC13) and explore the possibility of reduction of the scales. Methods: We analyzed the answers recorded for the QLQ-C30 and QLQ-LC13 in patients diagnosed with non-small-cell lung cancer (NSCLC) participating in 4 Cuban multicenter clinical trials. We assessed the dimensionality underlying both scales with a Mokken nonparametric item response analysis. We used the parametric Samejima’s graded response model to assess the item characteristics; we also conducted a confirmatory factor analysis (CFA) to test the dimensionality of both scales. Taking into account the previous results we compared different reduced scales using the Receiver Operator Curves (ROC Analysis). Results: 873 patients with NSCLC that completed the EORTC QLQ-C30 and 840 patients that completed the QLQ-LC13 were included. Mokken analysis of both scales resulted in 1-dimensional scales. All items showed scalability indices over 0.30. The overall scalability for the QLQ-C30 was 0.43, defining a medium scale according to Mokken’s criteria, while the overall scalability of the QLQ-LC13 was 0.44. Unconstrained Samejima’s graded response models showed appropriate fit, with most items of both scales presenting pertinent difficulty and discrimination parameters. The results of the CFA supported an underlying 1-dimensional latent structure for perceived quality of life (QLQ-C30 comparative fit index [CFI]=0.98; root-mean-square error of approximation [RMSEA]=0.05; QLQ-LC13 CFI=0.99 and RMSEA=0.04). All factor loadings were above 0.30. Conclusions: The QLQ-C30 and the QLQ-LC13 represent in patients with lung cancer a 1-dimensional structure of patient-perceived quality of life. All the reduced scales had similar performance compared with both original scales.