Rasch analysis of the PedsQL: an increased understanding of the properties of a rating scale

OBJECTIVE: Traditionally, measures have been developed using classical test theory (CTT). This study examines the psychometrics of the PedsQL 4.0 Generic Core Scales (parent report) using a modern psychometric approach (i.e., Rasch analysis) to determine if further insight regarding the behavior of the measure can be gained using a modern approach. STUDY DESIGN AND SETTING: Data from a Canadian study of 376 parents of children aged 2-17 years on active cancer treatment were analyzed using Rumm2030 software (RUMM Laboratory, Australia). RESULTS: Overall data did not fit the Rasch model and indicated important limitations in the PedsQL including disordered item thresholds, local dependency, and poor targeting. The internal consistency was higher using CTT (Cronbach's α=0.93) than Rasch (Person Separation Index=0.78). Rasch item curves showed that respondents did not discriminate between the five-point response categories and a three-point scale was easier to discriminate. CONCLUSIONS: The PedsQL is the most widely used generic measure of health-related quality of life in pediatrics. The use of Rasch allows detailed item-level evaluation and assists in identifying limitations of measures that could then be further explored. Studies are needed in other populations to better understand the behavior of the PedsQL from a modern psychometric perspective.