Defining chronic pain for epidemiological research: assessing a subjective definition

Chronic pain is an important cause of suffering, disability and loss of productivity. Despite this, little research has been done to quantify the problem in the community. This is partly due to the lack of an agreed definition of chronic pain. To address this we undertook a postal survey to test and validate a series of definitions of chronic pain for use in epidemiological research in the community. These definitions were based on duration of symptoms, with a subjective measure of severity in the seeking or taking of treatment for the symptoms. A series of seven definitions of increasing specificity was devised. A random sample of 400 patients was drawn from a general practice in Aberdeen and stratified for age, gender and receipt or non-receipt of regular analgesic drug prescriptions. Patients were surveyed by a self-completion questionnaire consisting of a definitional questionnaire, the SF-36 General Health Questionnaire, the Chronic Pain Grade questionnaire and a demographic section. A response rate of 76.3 per cent was obtained. Prevalence of chronic pain ranged from 9.9 to 80.9 per cent depending on the definition applied. Results for the SF-36 showed scores progressively lowering as definitions became more specific. The Chronic Pain Grade showed a similar result. We concluded that our criteria translate to a feasible, valid and acceptable method of defining and identifying chronic pain for research in the community.