| 翻訳と辞書 |
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 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, while a change from 20 to 80 would be a fold change of 4. 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).
A benefit of expressing a change as the ratio between an initial value and a final value – a fold change – is that the change itself is emphasized rather than the absolute values. For example, an absolute change of 100 is significant for an experiment with only 200 samples but negligible for an experiment with over a million samples. This property makes the fold change suitable for statistical tests that need to normalize data to eliminate systematic error. The distributional fold change test is based upon this idea.
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. A disadvantage to and serious risk of using fold change in this setting is that it is biased 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==
An error frequently occurs when an attempt is made to convert a fold change into a percentage change. Often an n-fold increase in a quantity will be reported as an increase. For example, a four-fold increase will often be reported as a 400-percent increase, which is incorrect. A four-fold increase is actually a 300-percent increase. This can be easily seen by examining the simple case of a two-fold increase. When a price increases from $1 to $2, it has experienced a two-fold increase and a 100% increase. In general, when a value increases -fold, it experiences an increase.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「fold change」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|