Establishing the minimal clinically important difference for the Questionnaire of Olfactory Disorders

Abstract

Background: Olfactory-specific quality of life (QOL) can be measured using the Questionnaire of Olfactory Disorders Negative Statements (QOD-NS). Changes in the QOD-NS after treatment can be difficult to interpret since there is no standardized definition of clinically meaningful improvement.

Methods: Patients with chronic rhinosinusitis (CRS) completed the QOD-NS. Four distribution-based methods were used to calculate the minimal clinically important difference (MCID): (1) one-half standard deviation (SD); (2) standard error of the mean (SEM); (3) Cohen's effect size (d) of the smallest unit of change; and (4) minimal detectable change (MDC). We also averaged all 4 of the scores together. Finally, the likelihood of achieving a MCID after sinus surgery using these methods, as well as average QOD-NS scores, was stratified by normal vs abnormal baseline QOD-NS scores.

Results: Outcomes were examined on 128 patients. The mean ± SD improvement in QOD-NS score after surgery was 4.3 ± 11.0 for the entire cohort and 9.6 ± 12.9 for those with abnormal baseline scores (p < 0.001). The MCID values using the different techniques were: (1) SD = 6.5; (2) SEM = 3.1; (3) d = 2.6; and (4) MDC = 8.6. The MCID score was 5.2 on average. For the total cohort analysis, the likelihood of reporting a MCID ranged from 26% to 51%, and 49% to 70% for patients reporting preoperative abnormal olfaction.

Conclusion: Distribution-based MCID values of the QOD-NS range between 2.6 and 8.6 points, with an average of 5.2. When stratified by preoperative QOD-NS scores the majority of patients reporting abnormal preoperative QOD-NS scores achieved a MCID.

Trial registration: ClinicalTrials.gov NCT02720653.

Keywords: minimal clinically important difference; olfaction; questionnaire of olfactory disorders; sinusitis.

Conflict of interest statement

Potential Conflicts of Interest: Zachary M. Soler is supported by grants from Entellus, Intersect, and Optinose, none of which are affiliated with this manuscript. Dr. Soler is a consultant for Olympus, which is not affiliated with this manuscript. Rodney J. Schlosser is supported by grants from OptiNose, Entellus and IntersectENT, none of which are associated with this manuscript. Dr. Schlosser is also a consultant for Olympus, Meda and Arrinex, which are not affiliated with this study. There are no disclosures for Jose Mattos or Timothy Smith.

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