Cross-cultural adaptation and psychometric properties of the European Portuguese version of the Global Perceived Effect Scale in patients with chronic low back pain

Purpose: To cross-culturally adapt the Global Perceived Effect Scale (GPES) into Portuguese and investigate its psychometric properties in patients with chronic low back pain. Methods: Cross-cultural adaptation was carried out according to published guidelines. Along with measures for pain and disability, GPES was administered at baseline, 48-h later and post-intervention. To estimate test-retest reliability, the intraclass correlation coefficient was used. The validity was examined through the correlation between the GPES and the Patient Global Improvement Change Scale and the contribution of baseline status to GPES scores. Responsiveness was assessed by analyzing hypotheses regarding areas under the curve and correlations with changes in other measures. Results: The test-retest reliability, the convergent validity and the contribution of the baseline status to GPES scores were demonstrated. The EPES correlated strongly with global perception of change (r = 0.677), and moderately with pain and disability changes (r = 0.457 and r = 0.452, respectively). Areas under the curve values of 0.71(95% CI = 0.607–0.825) and 0.83 (95% CI = 0.749–922) were found. Conclusion: The GPES demonstrated adequate psychometric properties. This study’s findings supported its use in clinical and research studies with patients with chronic low back pain.IMPLICATIONS FOR REHABILITATION The European Portuguese version of the Global Perceived Effect Scale demonstrated adequate reliability, validity and responsiveness. This instrument is suitable to evaluate meaningful changes in patients with chronic low back pain. The contribution of baseline status to GPES scores was confirmed by specific and recommended methods. The use of the GPES as external criterion of change in clinimetric studies was supported. The minimum important change was 2.5 points out of 11 of the GPES. Only improvements above this point should be considered as relevant to patients with chronic low back pain undergoing physiotherapy.