2.6. Statistical Analysis

Continuous variables are expressed as the mean ± standard deviation. Logarithmic transformation was applied to the data showing non-normal distribution. Group comparisons and trend were performed using the Student’s t-test, Pearson’s linear regression and one-way ANOVA. p < 0.05 was considered statistically significant. As mtDNA copy number displayed a non-linear distribution pattern, we changed it to a delta CT set for comparison; whereas oxidative stress markers displayed in a linear distribution. The contrast factor was applied in a one-way analysis of variances to test for linear trends displayed by the number of APOE4 allele number subgroups. Statistical analysis was performed using the Statistical Package for Social Science program (SPSS for Windows, version 11.5; SPSS, Chicago, IL, USA).