What Is Fold Change & logFC? | RNA-Seq Expression Analysis
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What is Fold Change?
Fold change is a measure of how much a quantity changes between two conditions. In gene expression analysis -- whether microarray or RNA-Seq -- it represents the ratio of expression levels between samples or groups.
What is logFC (Log Fold Change)?
Fold change is often expressed on a logarithmic scale. This log-transformed value is called log fold change (logFC or log2 fold change). Base 2 is the most common choice.
Examples of Fold Change and logFC
For example, if the mean expression level is 100 in the control group and 200 in the treatment group, the fold change is 2 and the logFC is 1.
| Gene Name | Average Expression Level in the Control Group | Average Expression Level in the Treatment Group | fold change | logFC |
| Gene A | 100 | 200 | 2 | 1 |
| Gene B | 100 | 400 | 4 | 2 |
| Gene C | 200 | 100 | 0.5 | -1 |
In gene expression studies using microarrays or RNA-Seq, volcano plots and MA plots are frequently used for visualization. The x-axis of a volcano plot and the y-axis of an MA plot both correspond to logFC.
Example of a Volcano Plot
Example of an MA Plot
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A research support company specializing in bioinformatics.
We provide tools and information to support life science research, with a focus on RNA-Seq analysis.