Dear Bioconductors I am using the package limma and understand that the type of background correction is important in the further processing of the data. Playing around with own data I found that using the "normexp" function with different values for the offset changes the final outcome of statistical testing. I am, therefore, a bit concerned about which is the best way to choose a value for the offset in "normexp". In the examples provided I found values of 25 or 50 but it was unclear to me why you would choose values in that range. Is there any rational in choosing a specific offset value other than just "playing around". In fact, what does the offset value mean? Offset from the background? Apologies if I didn't understand a simple principle here... Thanks for any help on this issue! Pie _______________________________________________________ Dr Pie Mueller Vector Research Division Liverpool School of Tropical Medicine Pembroke Place Liverpool L3 5QA UK Tel. +44 (0)151 705 3123 (office) Tel. +44 (0)151 705 3140 (Gwen Finnegan Dept Secretary) Fax. +44 (0)151 705 3369 http://www.liv.ac.uk/lstm/