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Review 2: "Evaluating the Effect of Olfactory Training on Improving the Sense of Smell in Patients with COVID-19 with Olfactory Disorders: A Randomized Clinical Trial Study"

Ultimately, the reviews grade this preprint not informative to potentially informative, and should not be viewed as actionable in its current state.

Published onAug 24, 2023
Review 2: "Evaluating the Effect of Olfactory Training on Improving the Sense of Smell in Patients with COVID-19 with Olfactory Disorders: A Randomized Clinical Trial Study"

RR:C19 Evidence Scale rating by reviewer:

Not informative. The flaws in the data and methods in this study are sufficiently serious that they do not substantially justify the claims made. It is not possible to say whether the results and conclusions would match that of the hypothetical ideal study. The study should not be considered as evidence by decision-makers.



Akbarpour et al’s paper explores the effects of six weeks of olfactory training on patients with smell dysfunction following COVID-19 infection. The QOD-NS Olfactory Disorders Questionnaire was used to measure smell function before and after the training. A control group was administered the questionnaire at the two time points.

We commend the authors for exploring this issue with a relatively large sample size. The strengths of this study are two-fold. First, it isolates olfactory training as the only intervention being evaluated so any effects observed cannot be attributed to other confounding interventions, e.g. corticosteroid treatments. Second, the call-to-action is very clear. The authors recommended that olfactory training be used as standard practice for COVID 19 patients with smell dysfunction and that this study is meant to be a model for the treatment plan.

Unfortunately, this recommendation is not actionable due to the weaknesses in the data collection and analysis. Olfactory training was only carried out for six weeks when comparable studies have tested the intervention for a minimum of three months. Additionally, the author’s choice to use the QOD NS Olfactory Disorders Questionnaire as the sole measurement tool greatly weakens the study. Although questionnaires can be valuable in understanding the qualitative feeling of patients, they rely on self-report, which is often at odds with measured test performance [1-4]. For example, Soter et al’s 2008 study reveals that focused questionnaire items are not meaningfully related to empirical testing when it comes to both smell and taste dysfunction [5].

As for data analysis, the control group has a mean age of 76 years, whereas the intervention group’s mean age is 45 years, making the two groups incomparable since olfaction is markedly decreased in older populations. Perhaps the authors could have controlled for age by using a more sophisticated statistical analysis, such as an analysis of covariance with age as the covariate. The p-values stated in Table 1 and 2 are also problematic. Akbarpour et al’s discussion section also indicates that another study that employed well-validated smell tests found no improvement after olfactory training. A more thorough discussion of why their results differ from those of that study would have strengthened this paper.

Our recommendation is that this study is Not Informative. In aggregate, the claims made in this paper are not substantially supported by the analysis that was done.


1. Doty, R.L., Olfactory dysfunction in COVID-19: pathology and long-term implications for brain health. Trends in Molecular Medicine, 2022. 28(9): p. 781-794.

2. Nordin, S., A.U. Monsch, and C. Murphy, Unawareness of smell loss in normal aging and Alzheimer's disease: discrepancy between self-reported and diagnosed smell sensitivity. The Journals of Gerontology: Series B, 1995. 50B(4): p. 187-192.

3. Singer-Cornelius, T., et al., Objective gustatory and olfactory dysfunction in COVID-19 patients: a prospective cross-sectional study. European Archives of Oto-Rhino-Laryngology, 2021. 278(9): p. 3325-3332.

4. Doty, R.L., D.A. Deems, and S. Stellar, Olfactory dysfunction in Parkinsonism: A general deficit unrelated to neurologic signs, disease stage, or disease duration. Neurology, 1988. 38(8): p. 1237-1244.

5. Soter, A., et al., Accuracy of self-report in detecting taste dysfunction. Laryngoscope, 2008. 118(4): p. 611-7.

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