Responsiveness of general health status in chronic low back pain: a comparison of the COOP Charts and the SF-36

The objective of this study was to compare the responsiveness and assess th e concurrent validity of two functional health status instruments, the Dart mouth COOP charts and the SF-36 in chronic low-back pain (CLBP) patients. T he data came from 129 of 174 patients who participated in a randomized clin ical trial of the therapeutic management of CLBP. Reliable and valid diseas e-specific outcomes, patient-rated low-back pain and disability, were used as external criteria (EC) to identify improved and non-improved patients. U npaired t-statistics and receiver operating characteristic (ROC) curve calc ulations were used to quantify responsiveness. The two instruments had suff icient and very similar responsiveness using both EC. Comparisons between i mproved and non-improved patients for the COOP charts and SF-36, respective ly, using pain as EC, yielded differences which translated into large effec t sizes (0.8 and 0.7) (P = 0.0008 and 0.003). Using disability as EC, diffe rences of moderate effect size were found (0.5 and 0.6) (P = 0.02 and 0.002 ). The ROC curve calculations using pain as EC resulted in areas under the curve of 0.76 (95% CI: 0.64, 0.88) for the COOP charts, and 0.74 (95% CI: 0 .60, 0.88) for the SF-36. The corresponding areas using disability as EC we re 0.67 (95% CI: 0.55, 0.79) and 0.72 (95% CI: 0.60, 0.84). The best cut-of f point in both instruments for differentiating between improved and non-im proved patients was approximately six percentage points. The constructs of functional health status, as reflected in the global scores of the two inst ruments, are highly correlated (r = 0.82). Six of the instruments' nine dim ensions are moderately to highly correlated (r = 0.52 to 0.86), and the ove rall canonical correlation was high (R = 0.9). In conclusion, both instrume nts seem equally suitable for use as outcome measures in clinical trials on CLBP. The COOP charts are faster to fill out and score. (C) 1999 internati onal Association for the Study of Pain. Published by Elsevier Science B.V.