Scoring based on item response theory did not alter the measurement ability of EORTC QLQ-C30 scales.
OBJECTIVE
Most health-related quality-of-life questionnaires include multi-item scales. Scale scores are usually estimated as simple sums of the item scores. However, scoring procedures utilizing more information from the items might improve measurement abilities, and thereby reduce the needed sample sizes. We investigated whether item response theory (IRT)-based scoring improved the measurement abilities of the EORTC QLQ-C30 physical functioning, emotional functioning, and fatigue scales.


METHODS
Using a database of 13,010 subjects we estimated the relative validities of IRT scoring compared to sum scoring of the scales.


RESULTS
The mean relative validities were 1.04 (physical), 1.03 (emotional), and 0.97 (fatigue). None of these were significantly larger than 1. Thus, no gain in measurement abilities using IRT scoring was found for these scales. Possible explanations include that the items in the scales are not constructed for IRT scoring and that the scales are relatively short.


CONCLUSIONS
IRT scoring of the three longest EORTC QLQ-C30 scales did not improve measurement abilities compared to the traditional sum scoring of the scales.
Petersen
Morten Aa
MA
The research unit, Department of Palliative Medicine, Bispebjerg Hospital, Bispebjerg bakke 23, 2400 Copenhagen, Denmark. map01@bbh.hosp.dk
Groenvold
Mogens
M
Aaronson
Neil
N
Brenne
Elisabeth
E
Fayers
Peter
P
Nielsen
Julie Damgaard
JD
Sprangers
Mirjam
M
Bjorner
Jakob B
JB
D000328:Adult; D016208:Databases, Factual; D004644:Emotions; D005221:Fatigue; D005260:Female; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009367:Neoplasm Staging; D009369:Neoplasms / Q000503:physiopathology / Q000523:psychology; D011788:Quality of Life; D015203:Reproducibility of Results; D018401:Sample Size; D011795:Surveys and Questionnaires