Statistical Analysis
Statistical analysis was performed with SPSS 19.0 (IBM SPSS Inc. Chicago, IL, USA). The normality of continuous variables were analysed by Shapiro-Wilk test. Descriptive statistics were reported as mean with standard deviation for continuous variables with normal distribution and as median with 25th-75th percentiles for those without. Categorical variables were reported as frequencies with percentages. Independent two-group comparisons for continuous variables without normal distribution, were tested using Mann-Whitney U test. For continuous variables with a normal data distribution, unpaired T-test was used. The proportions were compared between the groups using Pearson’s Chi-square test in case the assumptions were met. Otherwise, Fisher’s exact test was used. Due to biological relationship between aging and loss of renal function, a logistic regression analysis model including age and 2D-SWV of relevant portions (those with intergroup p<0.05) was constructed in order to predict the presence of Alb+ status. Significance level was accepted at p<0.05 for all statistical analyses.
A subgroup of a previous study included elasticity assessment of patients resembling our study population (17). Based on the mean SWV’s taken from that study, we performed an a priori sample size calculation using the prespecified alpha level of 0.05 and a beta level of 0.20 and an expected effect size of 0.20 (a relative %20 less SWV in healthy subjects as compared to diabetics). A total sample size of 28 was computed, we aimed to exceed 14 patients to be enrolled in each group. Moreover since it was planned to stratify the DM-II patients into two groups, the sample size of DM-II group was doubled.