hi, this is more of a statistical methodology question than an R question. however, since there are quite a few expert statisticians in this forum i think i can expect to get some useful feedback. here is my problem: i am studying a set of genes. for each gene i have a set of probes (there are 2-5 probes per gene). for each probe i have a set of 3 measurements (under conditions a, b and c). let us say that for a given gene i have 3 probes X, Y and Z. and for each probe there are 3 measurements, thus: a b c X Xa Xb Xc Y Ya Yb Yc Z Za Zb Zc for each gene i need to test the correlation among the measurements under each condition. so, are Xa, Ya, Za correlated AND Xb, Yb, Zb correlated AND Xc, Yc, Zc correlated? based on the degree of correlation among these probe measurements i will choose the genes for further study. of course i have to do this for each gene in my set of 100. what statistical tests do i need to perform to accomplish this? all advice will be appreciated. tia, anjan [[alternative HTML version deleted]]