Development of computerized adaptive testing (CAT) for the EORTC QLQ-C30 physical functioning dimension.
OBJECTIVE
Computerized adaptive test (CAT) methods, based on item response theory (IRT), enable a patient-reported outcome instrument to be adapted to the individual patient while maintaining direct comparability of scores. The EORTC Quality of Life Group is developing a CAT version of the widely used EORTC QLQ-C30. We present the development and psychometric validation of the item pool for the first of the scales, physical functioning (PF).


METHODS
Initial developments (including literature search and patient and expert evaluations) resulted in 56 candidate items. Responses to these items were collected from 1,176 patients with cancer from Denmark, France, Germany, Italy, Taiwan, and the United Kingdom. The items were evaluated with regard to psychometric properties.


RESULTS
Evaluations showed that 31 of the items could be included in a unidimensional IRT model with acceptable fit and good content coverage, although the pool may lack items at the upper extreme (good PF). There were several findings of significant differential item functioning (DIF). However, the DIF findings appeared to have little impact on the PF estimation.


CONCLUSIONS
We have established an item pool for CAT measurement of PF and believe that this CAT instrument will clearly improve the EORTC measurement of PF.
The Research Unit, Department of Palliative Medicine, Bispebjerg Hospital, Bispebjerg bakke 23, 2400, Copenhagen NV, Denmark. mpet0009@bbh.regionh.dk
Morten Aa
MA
Petersen
Mogens
M
Groenvold
Neil K
NK
Aaronson
Wei-Chu
WC
Chie
Thierry
T
Conroy
Anna
A
Costantini
Peter
P
Fayers
Jorunn
J
Helbostad
Bernhard
B
Holzner
Stein
S
Kaasa
Susanne
S
Singer
Galina
G
Velikova
Teresa
T
Young
D000203:Activities of Daily Living; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D051346:Mobility Limitation; D008960:Models, Psychological; D011594:Psychometrics; D011788:Quality of Life; D011795:Surveys and Questionnaires; D014584:User-Computer Interface; D055815:Young Adult