2.3. Statistical analysis
Statistical analysis was performed using GraphPad Prism software version 6.0f (San Diego, CA) and SPSS version 21 (IBM SPSS Statistics for Windows, Version 21.0, Armonk, NY). The normality of the data was checked for skewness and kurtosis, and was confirmed using the Shapiro–Wilk normality test. Dispersion and central tendency statistics were used to describe variables. A 2-tailed The sample size was calculated using G*power 3 (Heinrich Heine Universität Duesseldorf) according to the following parameters: Type I error 0.05, power 0.8, and effect size 0.43, based on previous observations.