
286 Statistics and Data Analysis for Microarrays Using R and Bioconductor
The normal distribution has several important characteristics as follows:
1. The distribution is symmetrical around the mean.
2. Approximatively 68% of the values are within 2 standard deviations
from the mean (i.e., less than 1 sta ndard deviation either to the left or
to the right of the mean: x − µ < ±σ).
3. Approximatively 95% of the values are within 4 standard deviations
from the mean (x − µ < ±2σ).
4. Approximatively 99% of the values are within 6 standard deviations
from the mean (x − µ < ±3σ).
5. The inflexion points of the curve (wher e the curve changes from bending
up ...