关于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 change is calculated simply as the ratio of the difference between final value and the initial value over 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).

In the field of genomics (and more generally in bioinformatics), fold changes are defined directly in terms of ratios.[8]
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If the initial value is A and the final value B, the fold change is defined as B/A. Note that this is different to the definition described above.
In other words, a change from 30 to 60 is defined as a fold-change of 2. This is also referred to as a "2-fold increase". Similarly, a change from 30 to 15 is referred to as a "2-fold decrease".

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