Fold change is a number describing how much a quantity changes going from an initial to a final value. For example, an initial value of 30 and a final value of 60 corresponds to a fold change of 2, or in common terms, a two-fold increase. Fold change is calculated simply as the ratio of the final value to the initial value, i.e. if the initial value is A and final value is B, the fold change is B/A. As another example, a change from 80 to 20 would be a fold change of 0.25. Some practitioners replace a fold-change value that is less than 1 by the negative of its inverse, e.g. a change from 80 to 20 would be a fold change of -4 (or in common terms, a four-fold decrease).

Fold change is often used in analysis of gene expression data in microarray and RNA-Seq

RNA-Seq

RNA-seq, also called "Whole Transcriptome Shotgun Sequencing" and dubbed "a revolutionary tool for transcriptomics", refers to the use of high-throughput sequencing technologies to sequence cDNA in order to get information about a sample's RNA content, a technique that is quickly becoming...

experiments, for measuring change in the expression level of a gene.

External links

• A comparison of fold-change and the t-statistic for microarray data analysis