Psychometric Validation of the Overall Symptom Severity Score for Chronic Rhinosinusitis

OBJECTIVE: Overall symptom severity (OSS) is a global metric of chronic rhinosinusitis (CRS) symptom severity. We sought to establish psychometric validity for the OSS, which has not been previously demonstrated in the literature. STUDY DESIGN: Prospective, observational. SETTING: Academic medical center. METHODS: Adult patients with CRS (N = 647) recruited and completed an OSS score (measured using a visual analog scale [VAS]), 22-item Sinonasal Outcome Test (SNOT-22), and 5-level EuroQol (EQ-5D) questionnaires. A subset of participants completed these questionnaires at a second time point to establish test-retest reliability (N = 65) and responsiveness to change (N = 225). Psychometric validation was performed by establishing criterion validity, test-retest reliability, and responsiveness in these CRS patients. RESULTS: The OSS score was significantly correlated with SNOT-22 (r = 0.73, 95% CI: 0.69-0.76, P < .001) and EQ-5D VAS scores (r = -0.39, 95% CI: -0.46 to -0.33, P < .001) at enrollment, demonstrating criterion validity. For the subset of participants who completed the OSS at a second time point ranging between 31 and 143 days later, the change in OSS was correlated with changes in SNOT-22 score (r = 0.72, 95% CI: 0.65-0.78, P < .001), and EQ-5D VAS (r = -0.30, 95% CI: -0.42 to -0.18, P < .001). The OSS score also demonstrated excellent test-retest reliability (r = 0.92, 95% CI: 0.87-0.95, P < .001). Using a distribution-based and four different anchor-based calculations, the minimal clinically important difference (MCID) for improvement and worsening for the OSS score was determined as ≥1.6 (or >1.5). CONCLUSION: The OSS score is a psychometrically valid measure of CRS symptom severity, with excellent criterion validity, test-retest reliability, and responsiveness. The MCIDs for improvement and worsening are proposed to be ≥1.6 (or >1.5).