Comparison of the Redundancy, Reliability, and Responsiveness to Change Among SF-36, Oswestry Disability Index, and Multidimensional Pain Inventory

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Abstract
To compare the Medical Outcomes Trust Short-Form-36 (SF-36), the Multidimensional Pain Inventory (MPI), and the Oswestry Disability Index (ODI) measures on internal consistency, domain overlap, and responsiveness in detecting changes following multidisciplinary pain treatment. 424 patients with chronic pain referred to a multidisciplinary pain center were assessed. Of these, 87 patients were assessed prior to and following treatment. Cronbach's alphas were calculated for each SF-36 and MPI domain, and for the ODI. Canonical correlation and regression analyses (R2) described overlap. Responsiveness to change was computed from treatment effect size and significance. Cronbach's alpha ranged from 0.69-0.92 for MPI domains, from 0.79-0.91 for SF-36 domains, and was 0.86 for the ODI. Three domains overlapped but several were unique (eg, the MPI "significant other" domains; R2 range 0.03-0.16). Significant changes following treatment were observed for the MPI Pain Severity, Interference and Outdoor Work Activities, the SF-36 Physical and Social Functioning, Bodily Pain, and the ODI. The MPI, SF-36, and ODI each have good psychometric properties. Three domains overlapped between the MPI and the SF-36: pain, Interference/Social functioning, and mental health. The MPI and the SF-36 each contributed unique domains such as the SF-36 General Health and Vitality domains and the MPI "significant other" and physical activity domains. Several of the MPI domains were among the most sensitive to change. Because of its large normative sample and samples of patients with diverse medical disorders, the SF-36 may be particularly useful to compare chronic pain patients to those with other medical conditions. The ODI has the lowest respondent burden. The MPI and SF-36, although containing much overlapping information, both make unique and complementary contributions to assessing patients with chronic pain.