In this study, we investigate how Wilks’ lambda, Pillai’s trace, Hotelling’s trace, and Roy’s largest root test statistics can be affected when the normal and homogeneous variance assumptions of the MANOVA method are violated. In other words, in these cases, the robustness of the tests is examined. For this purpose, a simulation study is conducted in different scenarios. In different variable numbers and different sample sizes, considering the group variances are homogeneous σ12=σ22=⋯=σg2 and heterogeneous (increasing) σ12<σ22<⋯<σg2, random numbers are generated from Gamma(4-4-4; 0.5), Gamma(4-9-36; 0.5), Student’s t(2), and Normal(0; 1) distributions. Furthermore, the number of observations in the groups being balanced and unbalanced is also taken into account. After 10000 repetitions, type-I error values are calculated for each test for α = 0.05. In the Gamma distribution, Pillai’s trace test statistic gives more robust results in the case of homogeneous and heterogeneous variances for 2 variables, and in the case of 3 variables, Roy’s largest root test statistic gives more robust results in balanced samples and Pillai’s trace test statistic in unbalanced samples. In Student’s t distribution, Pillai’s trace test statistic gives more robust results in the case of homogeneous variance and Wilks’ lambda test statistic in the case of heterogeneous variance. In the normal distribution, in the case of homogeneous variance for 2 variables, Roy’s largest root test statistic gives relatively more robust results and Wilks’ lambda test statistic for 3 variables. Also in the case of heterogeneous variance for 2 and 3 variables, Roy’s largest root test statistic gives robust results in the normal distribution. The test statistics used with MANOVA are affected by the violation of homogeneity of covariance matrices and normality assumptions particularly from unbalanced number of observations.

[Purpose] The effects of vitamin D on the circulating levels of IL-17 and IL-13 were investigated in patients with diabetic peripheral neuropathy, patients with diabetes mellitus type 2 without neuropathy, and healthy controls. [Subjects and Methods] A single-blind controlled clinical study was performed, including70 type 2 diabetic patients with or without diabetic peripheral neuropathy and 33 healthy volunteer controls. The 25(OH)D levels were evaluated using ultra-performance liquid chromatography, and IL-17 and IL-13 levels were assessed using enzyme-linked immunosorbent assays. [Results] The 25(OH) vitamin D concentration was lower in diabetic peripheral neuropathy patients than in diabetes mellitus patients without neuropathy and healthy controls. Similarly, 25(OH)D levels were lower in diabetes mellitus patients than healthy controls. IL-17 and IL-13 levels were higher in diabetes mellitus patients than in controls. Additionally, IL-13 levels were higher in diabetic peripheral neuropathy patients than in diabetes mellitus patients without neuropathy. These differences were statistically significant. There was a significant positive correlation between 25(OH)D and IL-13,and a negative correlation between 25(OH)D andIL-17 in the diabetic and diabetic neuropathy groups. [Conclusion] Vitamin D is a potential modifiable risk factor for diabetic peripheral neuropathy and may regulate inflammatory mediators, e.g., IL-17 and IL-13.

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