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Replication and validation of higher order models demonstrated that a summary score for the EORTC QLQ-C30 is robust
Johannes M. Giesinger, Jacobien M. Kieffer, Peter M. Fayers, Mogens Groenvold, Morten Aa. Petersen, Neil W. Scott, Mirjam A.G. Sprangers, Galina Velikova, Neil K. Aaronson, EORTC Quality of Life Group
Journal of Clinical Epidemiology, Available online 29 August 2015
To further evaluate the higher order measurement structure of the European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life Questionnaire Core 30 (QLQ-C30), with the aim of generating a summary score.
Study Design and Setting
Using pretreatment QLQ-C30 data (N = 3,282), we conducted confirmatory factor analyses to test seven previously evaluated higher order models. We compared the summary score(s) derived from the best performing higher order model with the original QLQ-C30 scale scores, using tumor stage, performance status, and change over time (N = 244) as grouping variables.
Although all models showed acceptable fit, we continued in the interest of parsimony with known-groups validity and responsiveness analyses using a summary score derived from the single higher order factor model. The validity and responsiveness of this QLQ-C30 summary score was equal to, and in many cases superior to the original, underlying QLQ-C30 scale scores.
Our results provide empirical support for a measurement model for the QLQ-C30 yielding a single summary score. The availability of this summary score can avoid problems with potential type I errors that arise because of multiple testing when making comparisons based on the 15 outcomes generated by this questionnaire and may reduce sample size requirements for health-related quality of life studies using the QLQ-C30 questionnaire when an overall summary score is a relevant primary outcome.
Health-related quality of life; Questionnaires; EORTC QLQ-C30; Measurement model; Higher order factor scores; Confirmatory factor analysis