The Rhinoplasty Rosetta Stone: using Rasch analysis to create and validate crosswalks between the NOSE and SCHNOS functional subscale.

ABSTRACT

BACKGROUND: The NOSE and SCHNOS functional subscale are widely used PROMs to measure functional outcomes of rhinoplasty. However, as different instruments produce scores on different metrics, results of these instruments cannot be linked directly. This hinders comparing and aggregating rhinoplasty outcome data from practices using either instrument. The aim of this study was to develop and validate crosswalks between the NOSE and SCHNOS-O. METHODS: In a sample of 552 rhinoplasty patients who completed both instruments, the NOSE and SCHNOS-O scales were co-calibrated onto a common interval-scaled metric using Rasch analysis. Separate Rasch models were run per instrument and the latent constructs were estimated using the calibrated item parameters. By anchoring original PROM scores of both instruments to this Rasch computed measurement scale, the scores of both instruments were linked. A second independent sample was used to validate the created crosswalks. RESULTS: Total scores on the NOSE and SCHNOS-O were strongly correlated. The Rasch-based co-calibration of the NOSE and SCHNOS-O items resulted in a model that adequately fitted the data. Back-and-forth crosswalk tables were created from the NOSE to the SCHNOS-O. For patients with moderate nasal obstruction, predicted SCHNOS-O scores were slightly higher for a given level of the NOSE. Intraclass correlation coefficients between predicted and actual scores were 0.93 for both directions, indicating adequate agreement for group-level comparisons. CONCLUSION: This study developed and validated Rasch-based crosswalks from the NOSE to the SCHNOS-O and vice-versa. The provided crosswalks enhance comparison and harmonization of functional rhinoplasty outcomes.