Statistics and Data Analysis for Microarrays Using R and Bioconductor, 2nd Edition

324 Statistics and Data Analysis for Microarrays Using R and Bioconductor

−3 −2 −1 0 1 2 3

0.0 0.1 0.2 0.3 0.4

x

y

FIGURE 10. 6: The shaded areas repre sent the values outside ±1 standard

deviation for a standard normal distribution.

the interva l to ± 2 standard deviations includes about 95% of the values. The

same information could have been o btained by asking what is the quantile

that co rresponds to a probability of 0.16 (which is half of 0.32, for the lower

tail of the distribution):

> qnorm(.16)

[1] -0.9944579

This quantile gives a value that is approximatively one standard deviation

to the left of the mean. In order to verify the same for the right ...