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


METHODS
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.


CONCLUSIONS
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.
Cieza
Alarcos
A
ICF Research Branch, WHO Collaborating Center for the Family of International Classifications, German Institute of Medical Documentation and Information, IHRS, Ludwig-Maximilian University, Munich, Germany.
Hilfiker
Roger
R
Boonen
Annelies
A
Chatterji
Somnath
S
Kostanjsek
Nenad
N
Ustün
Bedirhan T
BT
Stucki
Gerold
G
D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000503:physiopathology* / Q000534:rehabilitation; D001294:Attitude to Health; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care / Q000379:methods; D011594:Psychometrics; D011788:Quality of Life; D012720:Severity of Illness Index