A computer-adaptive disability instrument for lower extremity osteoarthritis research demonstrated promising breadth, precision, and reliability.
OBJECTIVE
To develop and evaluate a prototype measure (OA-DISABILITY-CAT) for osteoarthritis research using item response theory (IRT) and computer-adaptive test (CAT) methodologies.


METHODS
We constructed an item bank consisting of 33 activities commonly affected by lower extremity (LE) osteoarthritis. A sample of 323 adults with LE osteoarthritis reported their degree of limitation in performing everyday activities, and completed the Health Assessment Questionnaire-II (HAQ-II). We used confirmatory factor analyses to assess scale unidimensionality and IRT methods to calibrate the items and examine the fit of the data. Using CAT simulation analyses, we examined the performance of OA-DISABILITY-CATs of different lengths compared with the full-item bank and the HAQ-II.


RESULTS
One distinct disability domain was identified. The 10-item OA-DISABILITY-CAT demonstrated a high degree of accuracy compared with the full-item bank (r=0.99). The item bank and the HAQ-II scales covered a similar estimated scoring range. In terms of reliability, 95% of OA-DISABILITY reliability estimates were over 0.83 vs. 0.60 for the HAQ-II. Except at the highest scores, the 10-item OA-DISABILITY-CAT demonstrated superior precision to the HAQ-II.


CONCLUSIONS
The prototype OA-DISABILITY-CAT demonstrated promising measurement properties compared with the HAQ-II, and is recommended for use in LE osteoarthritis research.
Jette
Alan M
AM
Health & Disability Research Institute, Boston University School of Public Health, Boston, MA 02118, USA. ajette@bu.edu
McDonough
Christine M
CM
Haley
Stephen M
SM
Ni
Pengsheng
P
Olarsch
Sippy
S
Latham
Nancy
N
Hambleton
Ronald K
RK
Felson
David
D
Kim
Young-Jo
YJ
Hunter
David
D
D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D001294:Attitude to Health; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D004185:Disability Evaluation; D005260:Female; D017144:Focus Groups; D006801:Humans; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D015207:Osteoarthritis, Hip / Q000534:rehabilitation*; D020370:Osteoarthritis, Knee / Q000534:rehabilitation*; D017063:Outcome Assessment, Health Care / Q000379:methods; D011594:Psychometrics; D015203:Reproducibility of Results; D012985:Software Design