 In bioinformatics , microarrays are used to measure how strongly different genes are expressed in a sample of biological material . Different rates of expression of a gene are often compared by using the binary logarithm of the ratio of expression rates : the log ratio of two expression rates is defined as the binary logarithm of the ratio of the two rates . Binary logarithms allow for a convenient comparison of expression rates : a doubled expression rate can be described by a log ratio of 1 , a halved expression rate can be described by a log ratio of − 1 , and an unchanged expression rate can be described by a log ratio of zero , for instance . 
