We calculated allele and genotype frequencies and performed Hardy-Weinberg equilibrium tests for each b-AR genotype. The spectral HRV indices were log-transformed to produce normalized distributions. To control for the effects of non-genetic factors, differences in HRV variables were compared for individual genotypes using a general linear model (GLM) followed by the Bonferroni post hoc test for corrections of multiple between-group comparisons., using age, gender, and body mass index as covariates. Effect sizes were calculated with Cohen d, defined as the difference between the means of two groups, divided by the pooled standard deviation of these groups. Partial correlation analysis was applied, controlling for age and BMI, to determine the associations between standard HRV indices and nonrandomness index derived from the IBS method. A p value of less than 0.05 (two-tailed) was required for all statistical comparisons.