Use of item response theory to develop a shortened version of the EORTC QLQ-C30 emotional functioning scale
Accepted: 18 January 2004 DOI:
Cite this article as: Bjorner, J., Petersen, M., Groenvold, M. et al. Qual Life Res (2004) 13: 1683. doi:10.1007/s11136-004-7866-x Abstract Background: As part of a larger study whose objective is to develop an abbreviated version of the EORTC QLQ-C30 suitable for research in palliative care, analyses were conducted to determine the feasibility of generating a shorter version of the 4-item emotional functioning (EF) scale that could be scored in the original metric. Methods: We used data from 24 European cancer studies conducted in 10 different languages (n=8242). Item selection was based on analyses by item response theory (IRT). Based on the IRT results, a simple scoring algorithm was developed to predict the original 4-item EF sum scale score from a reduced number of items. Results: Both a 3-item and a 2-item version (item 21 ‘Did you feel tense?’ and item 24 ‘Did you feel depressed?’) predicted the total score with excellent agreement and very little bias. In group comparisons, the 2-item scale led to the same conclusions as those based on the original 4-item scale with little or no loss of measurement efficiency. Conclusion: Although these results are promising, confirmatory studies are needed based on independent samples. If such additional studies yield comparable results, incorporation of the 2-item EF scale in an abbreviated version of the QLQ-C30 for use in palliative care research settings would be justified. The analyses reported here demonstrate the usefulness of the IRT-based methodology for shortening questionnaire scales. Keywords Cancer IRT Palliative care Prediction Quality of Life Shortening of scales Abbreviations DIF
differential item functioning
a posteriori EF
European Organisation for Research and Treatment of Cancer
item information function
item response theory
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