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

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Abstract

Purpose

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.

Methods

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.

Results

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.

Conclusions

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.

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Authors and Affiliations

  1. Institution of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden

    Martin Ulander & Eva Svanborg

  2. Department of Clinical Neurophysiology, University Hospital, 581 85, Linköping, Sweden

    Martin Ulander, Eva Svanborg & Anders Broström

  3. Department of Medical and Health Sciences, Division of Nursing, Linköping University, Linköping, Sweden

    Kristofer Årestedt & Peter Johansson

  4. School of Human Sciences, Linnaeus University, Kalmar, Sweden

    Kristofer Årestedt

  5. Department of Cardiology, University Hospital, Linköping, Sweden

    Peter Johansson

  6. Department of Nursing Science, School of Health Sciences, Jönköping University, Jönköping, Sweden

    Anders Broström

Authors
  1. Martin Ulander
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  2. Kristofer Årestedt
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  3. Eva Svanborg
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  4. Peter Johansson
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  5. Anders Broström
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Correspondence to Martin Ulander.

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Ulander, M., Årestedt, K., Svanborg, E. et al. The fairness of the Epworth Sleepiness Scale: two approaches to differential item functioning. Sleep Breath 17, 157–165 (2013). https://doi.org/10.1007/s11325-012-0664-8

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  • DOI: https://doi.org/10.1007/s11325-012-0664-8

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