A z-score is a statistical measure of the relative expression of gene ontologies, and shows how much each ontology is over- or under-represented in a gene list. More specifically, the z-score is a standardized difference using the expected value and standard deviation of the number of genes meeting the criterion of a gene ontology term under a hypergeometric distribution [89]. Positive z scores indicate gene ontology terms with a greater number of genes meeting the criterion than is expected by chance, whereas negative z scores reflect gene ontology terms with fewer genes meeting the criterion than expected by chance. A z score near zero suggests that the number of genes meeting the criterion approximates the expected number [89]. Selected z-scores with values >2.0 or less than <-2.0 are reported for ontologies with ≥10 genes. Data were analyzed without transformation. In the table, the terms are: M Genes ↑ - number of genes up-regulated in human corneal epithelial cells of males (M), as compared to those of females (F); F Genes ↑ - number of genes up-regulated in human corneal epithelial cells of females, as compared to those of males; z-score - specific score for the up-regulated genes in the male and female cells.