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

466 Statistics and Data Analysis for Microarrays Using R and Bioconductor

drug administered, a nd the output is the expressio n level of the genes or, more

precisely, the difference between the expr ession levels of the genes without the

drug and the expression levels of the genes whe n the drug is administered.

There are situations in which the variance introduced by the various sources

is so great that the interesting effect, the gene regulation due to the drug, is

completely covered by the variation in the output determined by the other

sources of variance. In such circ ums tances, a preliminary study c an be un-

dertaken in order to assess the relative ...