Figure 2From: Normative references of heart rate variability and salivary alpha-amylase in a healthy young male populationHistograms of the interindividual variation of salivary alpha-amylase. From left to right, the distributions of raw, square root-, and natural logarithmic-transformed sAA values are presented. The histogram of raw amylase exhibited a markedly skewed distribution. Numerical transformations (square root and natural logarithm) improved skewness, although square root transformation appeared insufficient.Back to article page