Cross-cultural adaptation and validation of the Norwegian version of the Core Outcome Measures Index for low back pain

The Core Outcome Measures Index (COMI) is a short multidimensional scale covering all domains recommended to be included as outcome measures for patients with low back pain (LBP). The purpose of the present study was to translate and cross-culturally adapt the COMI into Norwegian and to test clinimetric properties of the Norwegian COMI version in patients with non-specific LBP recruited from various clinical settings. Ninety patients with non-specific LBP from primary care and hospital settings participated in the validation part and 61 also in the reproducibility part of the study (1 week apart). Acceptability, data quality, reproducibility and construct validity were investigated. The questionnaire was well accepted and with little missing data and end effects. Reliability in terms of intraclass correlations (ICC) was satisfactory for the COMI index [0.89 (95 % CI 0.82-0.94)] and most single-core items. Agreement was acceptable for the COMI index [standard error of measurement (SEMagreement) 0.80, minimal detectable change (MDCindividual) 2.21], but exceeded the minimal standard of acceptability in some of the individual core items. Construct validity was acceptable for the COMI index. The Norwegian version of the COMI index shows acceptable clinimetric properties in our patient population, but some of the sub-items had shortcomings. Our study, however, support the usefulness of the COMI index as an applicable stand-alone global scale when a light respondent burden is advisable.