Replication and validation of higher order models demonstrated that a summary score for the EORTC QLQ-C30 is robust.
OBJECTIVE
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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Division of Psychosocial Research and Epidemiology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Johannes M
JM
Giesinger
Division of Psychosocial Research and Epidemiology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Jacobien M
JM
Kieffer
Institute of Applied Health Sciences, University of Aberdeen, Foresterhill Road, AB25 2ZD Aberdeen, UK; Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Postboke 8905, N-7491 Trondheim, Norway.
Peter M
PM
Fayers
The Research Unit, Department of Palliative Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, 2400 Copenhagen, Denmark; Department of Public Health, University of Copenhagen, Øster Farimagsgade 5, 1014 Copenhagen, Denmark.
Mogens
M
Groenvold
The Research Unit, Department of Palliative Medicine, Bispebjerg Hospital, Bispebjerg Bakke 23, 2400 Copenhagen, Denmark.
Morten Aa
MA
Petersen
Institute of Applied Health Sciences, University of Aberdeen, Foresterhill Road, AB25 2ZD Aberdeen, UK.
Neil W
NW
Scott
Department of Medical Psychology, Academic Medical Centre, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
Mirjam A G
MA
Sprangers
Leeds Institute of Cancer and Pathology, St James's Institute of Oncology, University of Leeds, Beckett Street, LS9 7TF Leeds, UK.
Galina
G
Velikova
Division of Psychosocial Research and Epidemiology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. Electronic address: n.aaronson@nki.nl.
Neil K
NK
Aaronson
D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009369:Neoplasms / Q000628:therapy; D011788:Quality of Life; D011795:Surveys and Questionnaires
Confirmatory factor analysis; EORTC QLQ-C30; Health-related quality of life; Higher order factor scores; Measurement model; Questionnaires