My problem concerns categorizing patients to groups based on continuous variables. From the previous studies we know that there are continuous differences in mean expression of two signatures, which are negatively correlated. We are interested in comparing two extreme groups in terms of differentially expressed genes. Is there any statistical method for determining the cutoff from tha data? Maybe some measure of similarity we could use? Would it be reasonable to cluster patients based on those two signatures and in that way choose extreme groups?
Any advice will be appreciated.