Items from patient-oriented instruments can be integrated into interval scales to operationalize categories of the International Classification of Functioning, Disability and Health

J Clin Epidemiol. 2009 Sep;62(9):912-21, 921.e1-3. doi: 10.1016/j.jclinepi.2008.04.011. Epub 2009 Jul 9.


Objective: To exemplify the construction of interval scales for specified categories of the International Classification of Functioning, Disability and Health (ICF) by integrating items from a variety of patient-oriented instruments.

Study design and setting: Psychometric study using data from a convenience sample of 122 patients with rheumatoid arthritis. Patients completed six different patient-oriented instruments. The contents of the instrument items were linked to the ICF. Rasch analyses for ordered-response options were used to examine whether the instrument items addressing the ICF category b130: Energy and drive functions constitute a psychometrically sound interval scale.

Results: Nineteen items were linked to b130: Energy and drive functions. Sixteen of the 19 items fit the Rasch model according to the chi-square (chi(2)) statistic (chi(2)(df=32)=38.25, P=0.21) and the Z-fit statistic (Z(Mean)=0.451, Z(SD)=1.085 and Z(Mean)=-0.223, Z(SD)=1.132 for items and persons, respectively). The Person Separation Index r(beta) was 0.93.

Conclusion: The ICF category interval scales to operationalize single ICF categories can be constructed. The original format of the items included in the interval scales remains unchanged. This study represents a step forward in the operationalization and future implementation of the ICF.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Arthritis, Rheumatoid / physiopathology*
  • Arthritis, Rheumatoid / rehabilitation
  • Attitude to Health
  • Cross-Sectional Studies
  • Disability Evaluation
  • Female
  • Humans
  • Male
  • Middle Aged
  • Outcome Assessment, Health Care / methods
  • Psychometrics
  • Quality of Life
  • Severity of Illness Index*