Psychometric and Clinimetric Validity of the Modified 25-Item Sino-Nasal Outcome Test

Abstract

Background Productivity losses are a significant part of the disease burden associated with rhinosinusitis, but existing measures of disease-specific quality of life exclude explicit assessment of the impact of the disease on productivity. Objective The objective of this study was to evaluate the clinimetric and psychometric validity of the 25-item Sino-Nasal Outcome Test (SNOT-25), a modified version of the SNOT-22. Methods This was a prospective cohort study conducted at an academic medical center. Participants included adult patients with rhinosinusitis who presented for routine visits to the Washington University in St. Louis School of Medicine otolaryngology clinic between August 2016 and March 2017. Results The SNOT-25 was created with the addition of three productivity-specific items to the SNOT-22 instrument. A total of 120 rhinosinusitis patients completed all baseline measurements and 94 (78.3%) completed 3-month follow-up. The Cronbach’s α was 0.83, indicating high internal consistency. Rhinosinusitis patients had on average a 24-point higher baseline SNOT-25 score (95% confidence interval [CI]: 13–35) as compared to healthy controls indicating good discriminative validity. There was high correlation between SNOT-25 scores at 3 months and 3.5 months ( r = .81; 95% CI, 0.73–0.87) confirming strong test–retest reliability. SNOT-25 had a strong correlation with the overall score of the Nasal Obstruction Symptom Evaluation instrument ( r = .55; 95% CI, 0.42–0.65), and among Short Form-36 subscales, the strongest correlations existed between SNOT-25 and the fatigue scale ( r = −.522; 95% CI, −0.63 to −0.39). Exploratory factor analysis revealed that the 3 new questions of SNOT-25 loaded together with reduction in productivity and concentration items on a new “productivity” factor. Conclusion The SNOT-25 is a valid instrument that can be used to assess rhinosinusitis disease burden including the impact on productivity and may be a better predictor of treatment decisions and outcomes.