Reliability of the ICF core set for rheumatoid arthritis

Background: The comprehensive ICF Core Set for rheumatoid arthritis
(RA) is a selection of 96 categories from the International
Classification of Functioning, Disability and Health (ICF),
representing relevant aspects in the functioning of RA patients.
Objectives: To study the reliability of the ICF Core Set for RA in
rheumatological practice, and to explore the metric of the
qualifiers’ scale. Methods: 25 RA patients from an outpatient
department of rheumatology were interviewed using the ICF Core Set
for RA (76% females, mean (SD) age 57.5 (12.5) years, disease
duration 15.9 (14.6) years). Interviews were performed
independently by both a physiotherapist and an occupational
therapist on the same day and again after one week by one of them.
The severity of the patients’ problems was quantified on a
qualifier scale ranging from 0 (no problem) to 4 (complete
problem). Analyses of intra-rater and inter-rater agreement, kappa
statistics, and Rasch analyses were applied. Results: Mean
intra-rater (inter-rater) complete agreement for all categories was
seen in 59% (47%) of observations, ranging from 29% (0%) to 96%
(80%) for individual categories. Weighted kappa statistics with
value >0.4 showed reliability in 86% of categories within
raters, and in 43% of categories between raters. Improved
inter-rater and intra-rater reliability was observed with a reduced
number of qualifiers for the categories. Conclusions: Inter-rater
and intra-rater reliability of the ICF Core Set of RA was low to
moderate. The metric of the qualifiers’ scale may be improved by
reducing the number of qualifiers to three for all components.