(a) Log (base 10) of gene expression levels of 100 genes chosen using the Wilcox rank sum tests for the leukemias dataset. Darker spots indicate higher expression levels. The first 47 samples along the x-axis are ALL, the next 25 samples are AML. Genes are selected to best separate the two types of leukemias. (b) Plot of two latent factors estimated using the Rasch model for all 72 samples based on their gene expression profiles over 100 genes selected.