**7. Statistical analyses**

Statistical analysis was performed using SPSS for Windows (Statistical Package for the Social Sciences, version 20.0; SSPS Inc. Chicago, IL, USA). The normal distribution of the variables was evaluated using the Shapiro-Wilk test. The Mann-Whitney U test was used for the comparison of variables which were not normally distributed, and the independent Student's t-test for the comparison of variables which were normally distributed. The Pearson and Spearman tests were used for the evaluation of correlations among the variables according to the distribution of variables. P<0.05 was accepted as indicative of statistical significance. The results of variables with a normal distribution were expressed as mean ± SD and those with a non-Gaussian distribution were expressed as median (25th–75th percentile).
