Changes in chronic pain severity over time: the Chronic Pain Grade as a valid measure Alison M. Elliott a, * , Blair H. Smith a , W. Cairns Smith b , W. Alastair Chambers c a Department of General Practice, University of Aberdeen, Foresterhill Health Centre, Westburn Road, Aberdeen, AB25 2AY, UK b Department of Public Health, University of Aberdeen, Medical School, Foresterhill, Aberdeen, UK c Department of Anaesthetics, Aberdeen Royal In®rmary, Foresterhill, Aberdeen, UK Received 12 October 1999; received in revised form 1 May 2000; accepted 4 May 2000 Abstract Our understanding of the natural history of chronic pain in the community is 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 general population as a self-completion questionnaire. However, its reliability and validity for use in longitudinal studies and its responsiveness to change over time has not yet been assessed. We undertook a postal survey designed to test the responsiveness and the validity of the Chronic Pain Grade questionnaire over time. A random sample of 560 chronic pain patients, aged 25 years and over was drawn from an existing cohort and strati®ed for age, 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 change in health over time. To test whether changes in CPG scores correlated with changes in SF-36 scores, Spearman's rank correlation coef®cients were calculated. A response rate of 86% was achieved for the follow-up study. The majority of SF-36 scores changed in the hypothesized directions. Changes in CPG scores were signi®cantly correlated with changes in most of the SF-36 domains. We concluded that the CPG is a useful and valid objective instrument for measuring change in severity of chronic pain over time and could be used in longitudinal studies of chronic pain severity. q 2000 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. Keywords: Chronic pain; Pain measurement; Validation; Natural history; Epidemiology; Survey 1. Introduction Chronic pain is a common problem in the community. A recent population study in the UK estimated the prevalence in the general population to be 47% (Elliott et al., 1999). It is one of the commonest reasons for attending medical care and places signi®cant demands on the health service (Von Korff et al., 1990, 1991). It has been suggested that most chronic pain is currently assessed and managed inade- quately (Diamond, 1991). However, attempts at evaluation of treatment and management are confounded by our rela- tively poor understanding of the natural history of chronic pain. Previous studies of the natural history of chronic pain have tended to be relatively small and/or condition-speci®c (Potter and Jones, 1992; Magni et al., 1993; Macfarlane et al., 1996; Croft et al., 1998). A further problem has been with the research methodologies used. There is currently no validated measure of change in chronic pain over time. This has meant that previous studies have had to use unvalidated measurement instruments or have only been able to identify how many people still have chronic pain, not how their pain has changed over time. There is a clear need therefore for a validated measure of change in chronic pain over time. The Chronic Pain Grade questionnaire (CPG) (Von Korff et al., 1992) is a seven-item instrument that measures chronic pain severity in two dimensions: intensity and disability. It classi®es patients into ®ve hierarchical grades: Grade 0 (pain free), Grade I (low disability±low intensity), Grade II (low disability±high intensity), Grade III (high disability±moderately limiting) and Grade IV (high disabil- ity±severely limiting). The CPG was originally validated for use in the USA in interview-based research on patient samples representing sufferers of back pain, headache and temporo-mandibular disorder pain. It was recently tested for use in the UK when it was found to be acceptable, valid and reliable for use in a general population as a self-completion postal questionnaire (Smith et al., 1997). However, the relia- bility and validity of the CPG for use in longitudinal studies has not yet been assessed and its responsiveness to change Pain 88 (2000) 303±308 0304-3959/00/$20.00 q 2000 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved. PII: S0304-3959(00)00337-7 www.elsevier.nl/locate/pain * Corresponding author. Tel.: 144-1224-554228; fax: 144-1224- 840683. E-mail address: a.m.purves@abdn.ac.uk (A.M. Elliott).