Changes in chronic pain severity over time: the Chronic Pain Grade as a valid measure

Our understanding of the natural history of chronic pain in the community i s limited. This is partly due to the lack of a validated measure of chronic pain severity known to be responsive to change over time. The Chronic Pain Grade questionnaire has been shown to be valid and reliable for use in a g eneral population as a self-completion questionnaire. However, its reliabil ity and validity for use in longitudinal studies and its responsiveness to change over time has not yet been assessed. We undertook a postal survey de signed to test the responsiveness and the validity of the Chronic Pain Grad e questionnaire over time. A random sample of 560 chronic pain patients, ag ed 25 years and over was drawn from an existing cohort and stratified for a ge, gender and chronic pain severity. Subjects were re-surveyed by a postal self-completion questionnaire consisting of the Chronic Pain Grade and the SF-36 general health questionnaire, which is known to be responsive to cha nge in health over time. To test whether changes in CPG scores correlated w ith changes in SF-36 scores, Spearman's rank correlation coefficients were calculated. A response rate of 86% was achieved for the follow-up study. Th e majority of SF-36 scores changed in the hypothesized directions. Changes in CPG scores were significantly correlated with changes in most of the SF- 36 domains. We concluded that the CPG is a useful and valid objective instr ument for measuring change in severity of chronic pain over time and could be used in longitudinal studies of chronic pain severity. (C) 2000 Internat ional Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.