Response to “Letter to the editor regarding: ‘Self-administered transcranial direct current stimulation for pain in older adults with knee osteoarthritis: A randomized controlled study’ ”

Drs. Silvia-Filho and Pegado raised some concerns about our recent publication [[1]Martorella G. Mathis K. Miao H. Wang D. Park L. Ahn H. Self-administered transcranial direct current stimulation for pain in older adults with knee osteoarthritis: a randomized controlled study.Brain Stimul: Basic, Translational, and Clinical Research in Neuromodulation. 2022; 15: 902-909Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar] in their letter to the Brain Stimulation journal. However, with all due respect, their letter contains many conjectures and misunderstandings about statistics and/or our work. First, we carefully examined the data distribution before subsequent analysis, so we used the appropriate parametric test for Gaussian variables and non-parametric test for non-Gaussian variables, respectively (see the “Data analysis” section). Drs. Silvia-Filho and Pegado specifically mentioned that “when the distribution is skewed, tailed, or unknown, the Wilcoxon Rank Sum test can provide greater statistical power”; however, this is exactly what we did in our study, so it is difficult to understand the point of this suggestion. Second, Drs. Silvia-Filho and Pegado raised another concern by saying that “attention is advised when interpreting results due to the transformation of the variable from mean to rank.” They partially understand how the Wilcoxon rank-sum test works as such test does use ranks instead of the original variable values. However, the Wilcoxon rank-sum test does not do “transformation for the variable from mean to rank,” and the related transformation (definitely not “from mean to rank” though) is internal within the test itself so it will not affect other analyses [[2]Michael P.F. Michael A.P. Wilcoxon-Mann-Whitney or t-test? On assumptions for hypothesis tests and multiple interpretations of decision rules.Stat Surv. 2010; 4: 1-39PubMed Google Scholar,[3]Mann H.B. Whitney D.R. On a test of whether one of two random variables is stochastically larger than the other.Ann Math Stat. 1947; 18: 50-60Crossref Google Scholar]. The use of non-parametric for non-Gaussian variables is a standard practice; therefore, it is difficult to understand how the use of non-parametric tests can be connected to their concern that “the clinical applicability of the findings should be approached with caution.” Third, there is another concern about “data are controversial because, in Fig. 2, standard deviations are evidently overlapping in all moments, but not clearly represented.” Standard deviation overlapping does not necessarily suggest that differences between groups are insignificant. Fourth, about “the standard error is a dispersion measurement … not between groups”, we presented Fig. 2 in this way according to our manuscript reviewers' suggestions. Their concern about the use of standard error in Fig. 2 is largely a difference in personal preference between them and the manuscript reviewers. Fifth, the effect sizes were clearly reported in Table 2; therefore, it is not necessary to repeatedly report the same results also in Fig. 2. Finally, their concern of “The fact that the authors did not know the distribution of the data and decided to use a nonparametric test is an important limitation … prone to misinterpretation” is simply not a fact due to their lack of understanding of both our work and statistics.Table 2Comparison of pain intensity changes between two groups at 3 weeks and 3 months from baseline.VariableSham group (n = 60)Active group (n = 60)Effect size (d)Wilcoxon-StatisticP valueNRS Change (3-week)−1.08 ± 16.46−24.07 ± 21.551.202879.5<0.0001NRS Change (3-month)−0.43 ± 25.42−14.27 ± 24.940.552392.5<0.01WOMAC Change (3-week)−8.08 ± 10.56−10.95 ± 14.200.2321100.10WOMAC Change (3-month)−8.67 ± 14.64−8.92 ± 16.350.021912.50.56Note. Mean ± standard deviation is presented in the first two columns. NRS, Numeric Rating Scale; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index. Open table in a new tab Note. Mean ± standard deviation is presented in the first two columns. NRS, Numeric Rating Scale; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index. It should be mentioned that, during the review process of the original manuscript, we have carefully addressed all the statistical concerns of the manuscript reviewers. Note that none of the reviewers raised any illegitimate concerns like those in this letter. We welcome any further discussions to shed light on our work, but the concerns in this letter are not evidence-based or accurate and therefore will do little to enhance scientific rigor. Rather, their letter as written is likely to mislead readers rather than inform them. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Self-administered transcranial direct current stimulation for pain in older adults with knee osteoarthritis: A randomized controlled studyBrain Stimulation: Basic, Translational, and Clinical Research in NeuromodulationVol. 15Issue 4PreviewKnee osteoarthritis (OA) is a leading cause of pain in older adults. Previous studies indicated clinic-based transcranial direct current stimulation (tDCS) was effective to reduce pain in various populations, but no published studies have reported the efficacy of home-based self-administered tDCS in older adults with knee OA using a randomized clinical study. Full-Text PDF Open AccessLetter to the editor regarding: “Self-administered transcranial direct current stimulation for pain in older adults with knee osteoarthritis: A randomized controlled study”Brain Stimulation: Basic, Translational, and Clinical Research in NeuromodulationVol. 16Issue 3PreviewThe global population of individuals aged 65 years and older continues to rise, with a concomitant increase in the incidence of age-related pain conditions such as knee osteoarthritis [1]. Knee osteoarthritis is a debilitating condition that significantly impacts quality of life, increases mortality risk, and requires increased medication use [2]. Consequently, multiple clinical trials have been undertaken to identify effective pain management strategies. Full-Text PDF Open Access

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