Significance analysis of microarrays (SAM) is a widely used statistical technique, established in 2001 by Virginia Tusher, Robert Tibshirani and Gilbert Chu, for determining statistically significant changes in gene expression. With the advent of DNA microarrays, it is now possible to measure the expression of up to thousands of genes in a single hybridization experiment. The data generated is enormous, and a method for sorting out what is significant and what isn't is critical.