Differential item functioning (DIF) in the EORTC QLQ-C30: a comparison of baseline, on-treatment and off-treatment data

Neil William Scott, Peter Fayers, Neil K. Aaronson, Andrew Bottomley, Alexander de Graeff, Mogens Groenvold, Chad Gundy, Michael Koller, Morten A. Petersen, Mirjam A. G. Sprangers, on behalf of the EORTC Quality of Life Group and the Quality of Life Cross-Cultural Meta-Analysis Group

Research output: Contribution to journalArticlepeer-review

20 Citations (Scopus)


Introduction Differential item functioning (DIF) analyses can be used to explore translation, cultural, gender or other differences in the performance of quality of life (QoL) instruments. These analyses are commonly performed using "baseline" or pretreatment data. We previously reported DIF analyses to examine the pattern of item responses for translations of the European Organisation for Research and Treatment of Cancer (EORTC) QLQ-C30 QoL instrument, using only data collected prior to cancer treatment. We now compare the consistency of these results with similar analyses of on-treatment and off-treatment assessments and explore whether item relationships differ from those at baseline.

Methods Logistic regression DIF analyses were used to examine the translation of each item in each multi-item scale at the three time points, after controlling for the overall scale score and other covariates. The consistency of results at the three time points was explored.

Results For most EORTC QLQ-C30 subscales, the DIF results were very consistent across the three time points. Results for the Nausea and Vomiting scale varied the most across assessments.

Discussion The results indicated that DIF analyses were stable across each time point and that the same DIF effects were usually found regardless of the treatment status of the respondent.

Original languageEnglish
Pages (from-to)381-388
Number of pages8
JournalQuality of Life Research
Issue number3
Early online date27 Feb 2009
Publication statusPublished - Apr 2009

Bibliographical note

This work was funded by the EORTC Quality of Life Group, Cancer Research UK and the University of Aberdeen and carried out under the auspices of the EORTC Quality of Life Group


  • Differential item functioning
  • Pretreatment
  • On-treatment
  • Off-treatment
  • health applications


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