For example, if we want to test the above mentioned hypothesis, “Reduced expression of Apaf-1 in colorectal cancer correlates with high-grade phenotype.” by Fisher’s exact test, we have to investigate each number of cores in slides for four exclusive conditions : a) negative Apaf-1 expression and high-grade phenotype, b) negative Apaf-1 expression and low-grade phenotype, c) weak to strong Apaf-1 expression and high-grade phenotype, and d) weak to strong Apaf-1 expression and low-grade phenotype. This evidence concerns the gene APAF1 and colorectal cancer.