Psychometric properties of the brief version of the questionnaire of olfactory disorders in patients with chronic rhinosinusitis.

Background: The Questionnaire of Olfactory Disorders-Negative Statements (QOD-NS) is a 17-item instrument measuring olfactory-specific quality of life (QOL). However, in clinical research patients can be overwhelmed with multiple questionnaires. We recently developed the 7-item brief QOD-NS (B-QOD). Our objective was to evaluate the psychometric properties of the B-QOD in both the development (D) sample, and in a separate replication (R) sample.
Methods: Testing on D (n = 203) and R (n = 281) samples included initial exploratory factor analysis (EFA), followed by internal reliability, information loss, and confirmatory factor analysis (CFA). Finally, incremental predictive utility analysis (IPUA) was performed by correlating the B-QOD with the 22-item Sino-Nasal Outcome Test (SNOT-22) survey.
Results: EFAs of both D and R demonstrated an underlying single-factor structure (eigenvalue = 4.17 and 3.57, respectively) with comparable loading factors (R > 0.30 for both). B-QOD also had good internal reliability in both D and R (Cronbach's alpha = 0.88 and 0.83, respectively). Also, there is minimal information loss with B-QOD compared to QOD-NS in both D and R (R = 0.98 and 0.96, respectively). CFA indicates that the B-QOD single-factor model has good overall fit as measured by the Comparative Fit Index (CFI) and the Standardized Root Mean Squared Residuals (SRMSR) in the D and R samples (CFI = 0.99 and 0.97; SRMSR = 0.035 and 0.053). IPUA shows that the QOD-NS offers no additional predictive benefit of SNOT-22 scores when compared with B-QOD.
Conclusion: The 7-item B-QOD captures a structurally coherent and reliable single dimension, with minimal information loss and excellent external predictive utility when compared to the QOD-NS.
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