Fold change
Fold change is a measure 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 1 (or equivalently, a change to 2 times), or in common terms, a one-fold increase. Fold (meaning "times") change is calculated simply as the ratio of (the difference between final value and the initial value) and the original value. Thus, if the initial value is A and final value is B, the fold change is (B - A)/A or equivalently B/A - 1. As another example, a change from 80 to 20 would be a fold change of -0.75 , while a change from 20 to 80 would be a fold change of 3 (a change of 3 to 4 times the original).
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] A disadvantage to and serious risk of using fold change in this setting is that it is biased [2] and may miss differentially expressed genes with large differences (B-A) but small ratios (A/B), leading to a high miss rate at high intensities.
Converting a fold change to a percentage change
As with any conversion to percent, multiply the fold change by 100%.
