Prodinger B et al. – 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.Methods
- 256 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.
- 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.