# How to calculate fold change

How to calculate fold change. An easy way to think of fold changes is as ratios. The number of times something has changed in comparison to its original value.

The increases indicates that an amount doubled. Data can be examined for increments and decrements using fold change.

## How to calculate fold change The first thing you want to do here is to look at the original amount of a variable and compare it to the new amount.

This can be a fold change for an increase or a decrease, depending on whether the variable has been increased or decreased.

Divide this new amount by the original amount, and then make use of a calculator to multiply the two numbers together.

### Dividing the new amount

A fold change in quantity is calculated by dividing the new amount of an item by its original amount.

The calculation is 8/2 = 4 if you have 2 armadillos in a hutch and after breeding, you have 8 armadillos.

This means that there was a 4-fold increase in the number of armadillos (rather than an actual multiplication).

In this example, it may be better to illustrate that a fold change is based on per capita or per unit calculations instead of stating it as an actual multiplication.

### Division of the original amount

Under normal circumstances, one could simply take a 20g inventory at the start of an experiment and then run a 4g inventory later on to determine the fold change for a decrease.

However, if the initial amount (-20g) is abnormally high, it could skew the results. Thus, for the sake of accuracy, we recommend subtracting half of the original amount (10g) when calculating this answer instead.

### Look for the fold change Divide the experimental group’s data by that of the control group to calculate the fold change between the two groups.

The answer, for instance, would be 10/4 = 2.5 fold if you had a control group with 4 specimens and an experimental group with 10.

### Evolution of genomics and bioinformatics

In the field of gene sequencing (and more generally in bioinformatics) modern usage is to define fold change in terms of ratios and not by the alternative definition.

Log-ratios are often used for analysis and visualization of fold changes.

The log-base 2 is most commonly used, as it is easy to interpret, e.g., a doubling in the original scaling is equal to a log-fold change of 1, a quadrupling is equal to a log-fold change of 2, and so on.

Conversely, ratio measures are symmetric when corresponding changes decrease by an equivalent amount; e.g., halving is equal to a log-fold change of −1, quartering (−2), etc.

This results in more visually appealing graphs since changes are now represented linearly. On a graph axis displaying log2 fold changes, an 8-fold increase will be displayed as 3 (since 23 = 8).

There is, however, no mathematical reason to use logarithms only up to base 2, and due to many discrepancies in describing log2 fold changes in gene/protein expression, “loget” has been proposed.

### How is the fold difference calculated?

Fold change is computed simply as the ratio of changes between the final values and initial values over initial values.

Thus, if the initial value is X0 and the final value is X3, we have X3/X0 -1 or equivalently X3/(X0 -1).

### What is a fold change in statistics?

The fold change, also known as the log ratio, is a type of metric used in quantitative analysis. It expresses how two compared variables relate to each other by representing the ratio of their values.

The calculation multiplied one value by a fixed number before subtracting it from another value (hence “fold”), which is usually 1.

Fold changes are often used in analyzing data on gene expression like what happens to genes in response to an external change like DNA damage (which can lead cells to die) or ultraviolet radiation exposure that causes mutations that may lead to skin cancer development.

This data is measured through sequencing hearing genes in relation to genes that oversee cell death or cell cycle progression and regulation.

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