title: A computer-adaptive disability instrument for lower extremity osteoarthritis research demonstrated promising breadth, precision, and reliability.
abstract: 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.
authors.affiliation: Health & Disability Research Institute, Boston University School of Public Health, Boston, MA 02118, USA. ajette@bu.edu
authors.forename: Alan M
authors.initials: AM
authors.lastname: Jette
authors.forename: Christine M
authors.initials: CM
authors.lastname: McDonough
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Haley
authors.forename: Pengsheng
authors.initials: P
authors.lastname: Ni
authors.forename: Sippy
authors.initials: S
authors.lastname: Olarsch
authors.forename: Nancy
authors.initials: N
authors.lastname: Latham
authors.forename: Ronald K
authors.initials: RK
authors.lastname: Hambleton
authors.forename: David
authors.initials: D
authors.lastname: Felson
authors.forename: Young-Jo
authors.initials: YJ
authors.lastname: Kim
authors.forename: David
authors.initials: D
authors.lastname: Hunter
mesh_terms: 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