Hi I just want to do some simple survival analysis using TCGA expression data. I use survival package in R. Firstly I must divide the data into two parts. The one is patients with low expression of gene A and the other is patients with high expression of gene A. Then I plot the survival curve in R and calculate significant P value. The criterion to divide the data which I used is the mean value of mRNA expression value of whole data. My question is whether this criterion is suitable or not. Do you have some suggestions? Could you please give me some reference?