Hi, I am having trouble setting up the design for a microarray analysis. It involves 40 samples that are split into 4 groups and are treated in one of 2 ways. What I want to do is identify genes with an interaction effect between group and treatment. What would the best way to go about this? I have attempted the following: interDesign = model.matrix(~factor(sDrug) * factor(sGroup)) interFit = lmFit(lumi.N.P, interDesign) interCont = cbind(c(0,0,0,0,0,1,0,0),c(0,0,0,0,0,0,1,0),c(0,0,0,0,0,0,0,1)) interFit = contrasts.fit(interFit, interCont) interFit = eBayes(interFit) interDTest = decideTests(interFit, method="nestedF", adjust.method="fdr", p.value=0.05) which(abs(interDTest[,1]) == 1 | abs(interDTest[,2]) == 1 | abs(interDTest[,3]) == 1) Is this a suitable way to identify the genes with an interaction effect? So far, from looking at expression profiles, I don't seem to be picking out interesting genes.... Any help would be greatly appreciated. thanks, Sebastien

Hi Sebastien, Sebastien Gerega wrote: > Hi, > I am having trouble setting up the design for a microarray analysis. > It involves 40 samples that are split into 4 groups and are treated in > one of 2 ways. > What I want to do is identify genes with an interaction effect between > group and treatment. > What would the best way to go about this? I have attempted the following: > > interDesign = model.matrix(~factor(sDrug) * factor(sGroup)) > interFit = lmFit(lumi.N.P, interDesign) > interCont = cbind(c(0,0,0,0,0,1,0,0),c(0,0,0,0,0,0,1,0),c(0,0,0,0,0,0,0,1)) > interFit = contrasts.fit(interFit, interCont) > interFit = eBayes(interFit) > interDTest = decideTests(interFit, method="nestedF", > adjust.method="fdr", p.value=0.05) > which(abs(interDTest[,1]) == 1 | abs(interDTest[,2]) == 1 | > abs(interDTest[,3]) == 1) > > Is this a suitable way to identify the genes with an interaction effect? Well, with 4 groups and 2 treatments I get 6 total interactions. Are the three you are testing here the interesting interactions? > So far, from looking at expression profiles, I don't seem to be picking > out interesting genes.... Interesting defined how? The genes you get aren't a priori genes you want to see? Or you aren't getting any significant genes? Best, Jim > Any help would be greatly appreciated. > thanks, > Sebastien > > _______________________________________________ > Bioconductor mailing list > Bioconductor at stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/bioconductor > Search the archives: http://news.gmane.org/gmane.science.biology.informatics.conductor -- James W. MacDonald, M.S. Biostatistician Affymetrix and cDNA Microarray Core University of Michigan Cancer Center 1500 E. Medical Center Drive 7410 CCGC Ann Arbor MI 48109 734-647-5623