Rasch Analysis of the Pediatric Quality of Life Inventory 4.0 Generic Core Scales Administered to Patients With Duchenne Muscular Dystrophy

Abstract

Objectives: The objective of this study was to examine the psychometric properties of the Pediatric Quality of Life Inventory 4.0 Generic Core Scales (PedsQL 4.0 GCS) in Duchenne muscular dystrophy (DMD), a rare, severely debilitating, and ultimately fatal neuromuscular disease.

Methods: Patients with DMD were recruited from 20 centers across 9 countries as part of the Cooperative International Neuromuscular Research Group Duchenne Natural History Study (NCT00468832). The psychometric properties of the PedsQL 4.0 GCS were examined using Rasch analysis.

Results: In total, 329 patients with DMD (mean age 9 years, range 3-18 years, 75% ambulatory) completed the PedsQL 4.0 GCS. The most difficult instrument items, expressing the greatest loss in health-related quality of life, were those associated with emotional well-being (eg, being teased by other children, feeling sad, and not making friends), as opposed to somatic disability (eg, lifting heavy objects, participating in sports, and running). The mean item and person fit residuals were estimated at 0.301 (SD: 1.385) and -0.255 (1.504), respectively. In total, 87% (20 of 23) of items displayed disordered thresholds, and many exhibited nontrivial dependency. The overall item-trait interaction χ² value was 178 (115 degrees of freedom, P<.001). Our analysis also revealed significant issues with differential item functioning, and by investigating residual principal component loadings, the PedsQL 4.0 GCS total score was found to be multidimensional.

Conclusions: The PedsQL 4.0 GCS records information clinically relevant to patients with DMD, but the total scale score may not be fit for purpose as a measure health-related quality of life in this disease population.

Keywords: Cooperative International Neuromuscular Research Group; disability; patient-reported outcome; psychometric analysis; quality of life.