Reliability, validity, and responsiveness of the short form 12-item survey (SF-12) in patients with back pain

Study Design. Secondary analysis of data collected from spine patients' normal clinic visits from 1998 to 2001. Objective. To evaluate the reliability, validity, and responsiveness of the short form 12-item survey in patients with back pain. Summary of Background Data. The reliability, validity, and responsiveness of the short form 12-item survey in patients with back pain has not been previously evaluated. Methods. Patients were asked to complete a comprehensive computerized survey questionnaire during their regular clinic visits. A total of 2520 patients who indicated in their first surveys that they had back pain were included in the study of the reliability and validity of the short form 12-item survey. Of these, 506 patients completed another survey within 3 - 6 months of follow-up and were included in the responsiveness evaluation. Results. The two summary scales of the short form 12-item survey, physical component summary and mental component summary, demonstrated internal consistency reliability, with Cronbach alpha for both scales exceeding the recommended level of 0.70. Correlation of physical component summary and mental component summary with six other measures theoretically related or unrelated to these scales performed as expected without exception, demonstrating the construct validity of the short form 12-item survey. The responsiveness of the short form 12-item survey was supported by several pieces of evidence. First, the changes in physical component summary and mental component summary scores were correlated with the changes in back pain intensity. Second, for patients whose back pain improved, there was a significant increase in the follow-up physical component summary and mental component summary scores as compared to the baseline. Third, small to moderate effect size was observed for patients whose back pain became improved or became worse. Conclusions. The short form 12-item survey demonstrated good internal consistency reliability, construct validity, and responsiveness in patients with back pain.