Fold change

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 experiments, for measuring change in the expression level of a gene. [1]

Notes

  1. ^ Tusher, Virginia Goss; Tibshirani, Robert; Chu, Gilbert (2001). "Significance analysis of microarrays applied to the ionizing radiation response". Proceedings of the National Academy of Sciences of the United States of America 98 (18): 5116–5121. doi:10.1073/pnas.091062498. PMID 11309499. 

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