I am a "newcomer" to the field of microarray analysis and I have run into a snag trying to analyze some cdna data. To determine if the same gene in two different groups is differentially expressed I assume that I am comparing the expression levels of the two groups after normalization. However, when I use bioconductor to normalize the data (e.g., maNorm) I only end up with matrices of log ratios (maM). How do I compare the expression levels of the two groups if I only have the log ratios (and not the normalized expression levels). Thanks for any help that you can provide. Rob. ********************************************************************** ****** Robert A. Cribbie Assistant Professor Associate Coordinator Department of Psychology Statistical Consulting Service York University Institute for Social Research Toronto, Ontario, Canada York University M3J 1P3 Phone: 416-736-5115 (x88615) E-Mail: cribbie@yorku.ca Fax: 416-736-5814 Website: http://www.psych.yorku.ca/cribbie