I am working on elucidating pathologically relevant miRNAs responsible for disease progression and chemoresistance in chronic lymphocytic leukemia. For differential expression of miRNAs I am using the edgeR package. I am new to statistics, edger and any help would be highly appreciated. The samples are classified as 1) Indolent which has 7 patient samples 2) Chemo-responsive, 9 patient samples 3) Non-responsive, 7 patient samples 4) Control, 2 samples. I want to check the differential expression of miRNAs as follows: (a) Control vs Indolent+Chemo-responsive+ Non-responsive (b) Indolent vs Chemo-responsive+ Non-responsive (c) Indolent vs Chemo-responsive (d) Indolent vs chemo-responsive. I went through the user guide of edgeR and in section 3.2.3 GLM approach by using contrast argument of glmLRT contrast(-1,1,0) will compare B to A sample. This works well when comparing two groups. How do I work when I have to compare A vs B+C and A vs B+C+D.