Measuring Functioning in People with Fibromyalgia (FM) Based on the International Classification of Functioning,Disability and Health (ICF)—A Psychometric Analysis |
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| Authors: | Birgit Prodinger MSc Thomas Salzberger Dr. Mag. Gerold Stucki MD MS Tanja Stamm PhD Dr. Mag. MBA MSc Alarcos Cieza PhD MPH |
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| Affiliation: | 1. Clinic for Internal Medicine III, Department of Rheumatology, Medical University of Vienna, Austria;2. Institute for Marketing, Vienna University of Economics and Business, Austria;3. Department Health Sciences and Health Policy, University of Lucerne, Switzerland;4. ICF Research Branch in Cooperation with the WHO Collaborating Centre for the Family of International Classifications in Germany (at DIMDI)1;5. Swiss Paraplegic Research (SPF), Nottwil, Switzerland;6. ICF Research Branch in Cooperation with the WHO Collaborating Centre for the Family of International Classifications in Germany (at DIMDI)1;7. Institute for Health and Rehabilitation Sciences, Research Unit for Biopsychosocial Health, Ludwig‐Maximilians‐Universit?t, Munich, Germany |
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| Abstract: | Objectives: Instruments to assess functioning in patients with FM vary considerably in their content and are often symptom‐specific. This study aimed to examine whether it is feasible to construct a psychometric‐sound clinical instrument to measure functioning in FM based on the Brief ICF‐Core‐Set for chronic widespread pain (CWP). Methods: Two hundred and fifty six people with FM completed the Brief ICF‐Core‐Set. The Rasch model was used for analysis. Once ordering of response options of ICF categories was ensured, the following properties were studied: fit of the ICF categories to the Rasch model, the targeting between ICF categories and a person’s abilities, unidimensionality, and reliability. Results: Six ICF categories were rescored due to disordered thresholds. Five ICF categories were removed due to high model‐misfit and differential item functioning (DIF) for gender. Scores from 46 participants were excluded due to extreme scores. The ICF categories included display consistency with an underlying unidimensional construct, are free of DIF for age, disease duration and gender, display excellent overall reliability, and cover a range of functioning difficulties. Conclusions: This study illustrates that it is possible to measure functioning as a unidimensional construct based on selected ICF categories from the components body functions, as well as activities and participation of the Brief ICF‐Core‐Set for CWP in patients with FM. |
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| Keywords: | Rasch analysis item‐response theory outcomes research rehabilitation chronic pain |
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