Reliability and validity of the Italian version of the Chronic Pain Grade questionnaire in patients with musculoskeletal disorders.

The aim of this study is to analyse the psychometric properties of the Italian version of the Chronic Pain Grade (CPG) questionnaire within a population of chronic musculoskeletal pain patients. The CPG questionnaire was adapted following the translation and back-translation methodologies. There were 576 patients with chronic musculoskeletal pain. Internal consistency was checked by the Cronbach's alpha coefficient. Construct validity was analysed by performing principal component factor analysis and by comparing CPG dimensions and subscales with the SF-36 questionnaire. Discriminant validity was assessed by comparing the CPG and SF-36 dimensions in patients with and without other health conditions. Factor analysis yielded two factors which accounted for 76.4% of the variance of the questionnaire. Both subscales of the CPG showed satisfying to good internal consistency. Cronbach's alpha was 0.89 for the first factor 'Disability Score' (58.72% of the explained variance) and 0.81 for the second factor 'Characteristic Pain Intensity' (17.70% of the explained variance). Item-total correlations for the subscales were moderate up to high (from 0.500 to 0.771). In comparison with the SF-36, the expected correlations were found when comparing items measuring similar constructs, supporting the concepts of convergent construct validity. Discriminant validity, assessed by comparing the CPG dimensions in patients with and without other health conditions, showed that the CPG shows moderate association with the presence of co-morbidities. Furthermore, the CPG Disability Score was inversely correlated (p=0.01) to years of formal education. In conclusion, the Italian version of the CPG questionnaire has shown to be valid and reliable for evaluating the severity of chronic musculoskeletal pain, with metric properties in agreement with the original, widely used version.