Validation of a minimum outcome core set in the evaluation of patients with back pain

Study Design. Prospective study of patients with subacute osteoporotic fracture (SOF) or chronic low back pain (CLBP). Objective. To evaluate reliability, validity, and responsiveness of a purposefully brief outcome instrument. Summary of Background Data. A minimum standardized "core set" was proposed for monitoring patients with low back pain in 1998, but an assessment of metric properties was still lacking. Methods. The Core Set, SF-36, and Oswestry questionnaires were completed by 154 patients. Test-retest reproducibility was evaluated in a subsample of 43 stable patients with CLBP. Responsiveness was evaluated by estimating effect size (ES) of pre-postsurgery changes in 50 patients with SOF and 23 with CLBP. Results. The total Core Set showed good reproducibility with intraclass correlation coefficients on test-retest near the highest standard of 0.9, whereas internal consistency differed between patients with CLBP and those with SOF (Cronbach's alpha of 0.92 and 0.64, respectively). Most correlations of the Core Set with SF-36 and Oswestry, previously hypothesized as high, were > 0.65, demonstrating good construct validity. Sensitivity to change of the Core Set (ES 0.4-2.3) is similar to the Oswestry (ES 0.7 and 2.3). Conclusions. These findings support the potential usefulness of the Core Set when respondent burden is a major concern. However, subscale scores need to be further tested in other populations before they can be widely recommended.