Concurrent evaluation of data quality, internal consistency, test-retest reliability and validity of two patient-reported outcome measures (PROMs) for measuring functional impairment in hand OA (HOA); the Australian/Canadian Osteoarthritis Hand Index (AUSCAN; 15 items) and the Functional Index of HOA (FIHOA; 10 items).
Patients from an HOA cohort [n=128, mean age 68.6 (s.d. 5.8) years, 91% women] completed PROMs and performance measures during routine follow-up. One week later, a subsample (n=40) reporting no change on an HOA-specific transition question contributed with test-retest data.
Both instruments had satisfactory levels of data quality, internal consistency, test-retest reliability and construct validity. The AUSCAN performed slightly better than the FIHOA relating to levels of missing data (0 vs 5%), floor effects, principal component analysis loadings (0.62-0.83 vs 0.52-0.83), item-total correlation (0.77-0.91 vs 0.45-0.76) and Cronbach's α (0.94-0.96 vs 0.90), respectively. AUSCAN items had slightly lower test-retest κ-values (0.29-0.77 vs FIHOA 0.41-0.77) and AUSCAN scales lower intra-class correlations (0.80-0.92 vs FIHOA 0.94). Correlations between the two instruments ranged from 0.58 to 0.88 for the AUSCAN scales of stiffness and physical function, respectively. AUSCAN physical function scale was generally slightly strongly correlated with the other PROMS and performance measures.
The AUSCAN and the FIHOA are reliable and valid instruments suitable for measuring physical functioning in HOA. The FIHOA had higher test-retest reliability and is shorter, but the AUSCAN performed slightly better concerning data quality and construct validity.