Quality of Life Research

, Volume 18, Issue 8, pp 1125–1130

The practical impact of differential item functioning analyses in a health-related quality of life instrument

  • Neil W. Scott
  • Peter M. Fayers
  • Neil K. Aaronson
  • Andrew Bottomley
  • Alexander de Graeff
  • Mogens Groenvold
  • Chad Gundy
  • Michael Koller
  • Morten A. Petersen
  • Mirjam A. G. Sprangers
Article

DOI: 10.1007/s11136-009-9521-z

Cite this article as:
Scott, N.W., Fayers, P.M., Aaronson, N.K. et al. Qual Life Res (2009) 18: 1125. doi:10.1007/s11136-009-9521-z

Abstract

Introduction

Differential item functioning (DIF) analyses are commonly used to evaluate health-related quality of life (HRQoL) instruments. There is, however, a lack of consensus as to how to assess the practical impact of statistically significant DIF results.

Methods

Using our previously published ordinal logistic regression DIF results for the Fatigue scale of a HRQoL instrument as an example, the practical impact on a particular Norwegian clinical trial was investigated. The results were used to determine the difference in mean Fatigue scores assuming that the same trial was conducted in the UK. The results were then compared with published information on what would be considered a clinically important change in scores.

Results

The item with the largest DIF effect resulted in differences between the mean English and Norwegian Fatigue scores that, although small, could be considered clinically important. Sensitivity analyses showed that larger differences were found for shorter scales, and when the proportions in each response category were equal.

Discussion

Our scenarios suggest that translation differences in an item can result in small, but clinically important, differences at the scale score level. This is more likely to be problematic for observational studies than for clinical trials, where randomised groups are stratified by centre.

Keywords

Differential item functioningQuality of lifeClinical importanceClinical trials

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  • Neil W. Scott
    • 1
  • Peter M. Fayers
    • 1
    • 2
  • Neil K. Aaronson
    • 3
  • Andrew Bottomley
    • 4
  • Alexander de Graeff
    • 5
  • Mogens Groenvold
    • 6
    • 7
  • Chad Gundy
    • 3
  • Michael Koller
    • 8
  • Morten A. Petersen
    • 6
  • Mirjam A. G. Sprangers
    • 9
  1. 1.Section of Population Health, Institute of Applied Health SciencesUniversity of AberdeenAberdeenUK
  2. 2.Department of Cancer Research and Molecular Medicine, Faculty of MedicineNorwegian University of Science and TechnologyTrondheimNorway
  3. 3.Division of Psychosocial Research and EpidemiologyNetherlands Cancer InstituteAmsterdamThe Netherlands
  4. 4.Quality of Life DepartmentEuropean Organisation for Research and Treatment of Cancer HeadquartersBrusselsBelgium
  5. 5.Division of Medical Oncology, Department of Internal MedicineUniversity Medical CentreUtrechtThe Netherlands
  6. 6.Department of Palliative MedicineBispebjerg HospitalCopenhagenDenmark
  7. 7.Institute of Public HealthUniversity of CopenhagenCopenhagenDenmark
  8. 8.Centre for Clinical StudiesUniversity Hospital RegensburgRegensburgGermany
  9. 9.Department of Medical Psychology, Academic Medical CentreUniversity of AmsterdamAmsterdamThe Netherlands