The comprehensive osteoarthritis test: a simple index for measurement of treatment effects in clinical trials.
OBJECTIVE
To assess the measurement properties of a simple index of symptom severity in osteoarthritis (OA) of the hips and knees.


METHODS
Both the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the proposed new Comprehensive Osteoarthritis Test (COAT) instrument were completed weekly by 125 subjects in the context of a randomized, 12-week, 3 parallel-arm clinical trial. The reliabilities of the various scales were assessed on a weekly basis by use of Cronbach's alpha coefficients. The validity of the COAT total scale was assessed by correlation with the WOMAC total scale on a weekly basis with correlation coefficients, and in terms of the correlations between subject-level intercepts and slopes over time. The relative responsiveness of the WOMAC and COAT total scales was assessed using a multilevel (longitudinal) multivariate (WOMAC, COAT) linear model.


RESULTS
The WOMAC and COAT total scales were highly reliable (mean over weeks: WOMAC alpha = 0.98; COAT alpha = 0.97). The correlations between the WOMAC and COAT scales were very high (mean over weeks = 0.92; subject-level intercepts = 0.91, slopes = 0.88). The COAT total scale was significantly more responsive than the WOMAC total scale in the active treatment (34.8% improvement vs 26.8%; p = 0.002).


CONCLUSIONS
The COAT total scale is simple to administer, reliable, valid, and responsive to treatment effects.
Brooks
Lyndon O
LO
Australian Centre for Complementary Medicine Education and Research, University of Queensland, Brisbane, Australia. lbrooks@scu.edu.au
Rolfe
Margaret I
MI
Cheras
Phillip A
PA
Myers
Stephen P
SP
D018501:Antirheumatic Agents / Q000627:therapeutic use; D002986:Clinical Trials as Topic / Q000379:methods; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D010003:Osteoarthritis / Q000175:diagnosis* / Q000188:drug therapy; D010147:Pain Measurement / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D012720:Severity of Illness Index
D018501:Antirheumatic Agents