Sleep and Breathing

, Volume 17, Issue 1, pp 157–165 | Cite as

The fairness of the Epworth Sleepiness Scale: two approaches to differential item functioning

  • Martin UlanderEmail author
  • Kristofer Årestedt
  • Eva Svanborg
  • Peter Johansson
  • Anders Broström
Original Article



Differential item functioning (DIF) is said to exist in an item if a subject’s response to the item is affected by other aspects than that which the test is intended to assess. DIF might affect the validity of a test. The aim of this study was thus to examine whether any of the items in the Epworth Sleepiness Scale (ESS) exhibits DIF regarding age or gender, and if so, to which degree.


Using previously collected cross-sectional ESS data from 1,168 subjects with different clinical characteristics (61% males, mean age 67.8 year (SD 12.2 year)), ordinal regression as well as Rasch-based DIF analyses were performed.


Concerning age, both DIF analyses showed DIF for age in items 3 (inactive in a public place), 4 (passenger in a car), and 8 (in a car that has stopped in traffic). The Rasch model also showed DIF for gender in item 3. The DIF magnitudes as judged by McFadden pseudo-R 2 changes were, however, only minor.


ESS has small but reproducible DIF for age in items 3, 4, and 8. The detected DIF might be worth to consider in large-sample studies, although it probably has no effect on an individual basis.


Epworth Sleepiness Scale Differential item functioning Sleep Daytime sleepiness 


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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Martin Ulander
    • 1
    • 2
    Email author
  • Kristofer Årestedt
    • 3
    • 4
  • Eva Svanborg
    • 1
    • 2
  • Peter Johansson
    • 3
    • 5
  • Anders Broström
    • 2
    • 6
  1. 1.Institution of Clinical and Experimental MedicineLinköping UniversityLinköpingSweden
  2. 2.Department of Clinical NeurophysiologyUniversity HospitalLinköpingSweden
  3. 3.Department of Medical and Health Sciences, Division of NursingLinköping UniversityLinköpingSweden
  4. 4.School of Human SciencesLinnaeus UniversityKalmarSweden
  5. 5.Department of CardiologyUniversity HospitalLinköpingSweden
  6. 6.Department of Nursing Science, School of Health SciencesJönköping UniversityJönköpingSweden

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