What does the chronic pain grade questionnaire measure?

This study explored the ability of the Chronic Pain Grade Questionnaire (CPG) to operationalise the WHO's model of health outcomes, namely the International Classification of Functioning, Disability and Health (ICF). Twelve expert judges used the method of discriminant content validation to allocate the seven items of the CPG to one or more ICF outcome, namely, impairment, activity limitations and participation restrictions. One-sample t-tests classified each item as measuring impairment, activity limitations or participation restrictions, or a combination thereof. The results indicated that the CPG contains items able to measure each of the three ICF outcomes. However, the pain grade classification system used in the CPG conflates the ICF outcomes. The implication of this conflation of outcome for the assessment of interventions is discussed.