Abstract
The rank product statistic has been widely used to detect differentially expressed genes in replicated microarrays and a one-class setting. The objective of this article is to apply a rank product statistic to approximate the P-value of differential expression in a two-class setting, such as in normal and cancer cells. For this purpose, we introduce a simple statistic that compares the P-values of each class's rank product statistic. Its null distribution is straightforwardly derived using the change-of-variable technique.