Towards Standardized Assessment of Outcomes in Back Pain-Validation of Linking Studies Between Disease-Specific and...

Background: Comparing outcomes across different health measurement tools is essential where various patient-reported outcome measures (PROMs) are used. In spinal surgery, where recent studies show that over 30 different PROMs are applied, this need becomes even more pressing. Although several statistical transformations between the Oswestry Disability Index (ODI) and the PROMIS Profile 29 have been proposed, validation studies on conversion equations and cross-walk tables remain limited. In this study, we examined the agreement between observed ODI scores and those predicted from the PROMIS Profile 29 in a large sample of patients with low back pain, collected from routine clinical care. Methods: We compared the performance of regression and linking models at both the individual and group levels. Using Bland-Altman plots, we assessed the mean difference, 95% limits of agreement, root mean squared error (RMSE), and standardized mean differences (Cohen's d) between predicted and observed ODI scores. Results: While group-level agreement was satisfactory, with negligible effect sizes, individual prediction accuracy was relatively poor. Additionally, regression models showed inconsistent performance across the ODI score range, though incorporating more domains marginally improved predictions. Conclusions: The equipercentile linking approach demonstrated stable agreement across all ODI scores, making it the preferred method. Future regression models should account for nonlinear relationships between PROMs to enhance prediction accuracy.