The Chronic Pain Grade questionnaire: validation and reliability in postal research

The Chronic Pain Grade questionnaire has been proposed as an interview-administered, multi-dimensional measure of chronic pain severity in selected populations with chronic pain in the United States of America. It has not previously been tested in the United Kingdom, in self-completion form or in an unselected general population. We undertook a postal survey to assess its reliability, validity and acceptability in these circumstances, using a general practice population in Scotland, with a practice population of 11202 patients. A random sample of 400 patients aged over 18 was drawn, stratified for age, gender and receipt or non-receipt of regular prescriptions for pain-relieving medication. The dimensions and sub-scales of the Chronic Pain Grade were compared with the SF-36 general health questionnaire and questions relating to duration of any pain and attempts to seek treatment for this. The methodological approach proposed by Streiner and Norman (1989) was used to assess validity and reliability. A response rate of 76% was achieved. Cronbach's alpha was > 0.9 and item-total correlations were all high, indicating good internal consistency and reliability. Validity was confirmed by psychometric testing, including confirmatory factor analysis. Good correlations with comparable dimensions of the SF-36 general health questionnaire confirmed convergent validity. Construct validity was confirmed by testing scores against duration of pain and treatment sought for pain. We concluded that the Chronic Pain Grade questionnaire is a useful, reliable and valid measure of severity of chronic pain. It translates well into UK English and is acceptable in general population postal research.