## Introduction

In data mining, information gain is a measure of the expected reduction in entropy (information content) that results from knowing the value of a specific attribute. The greater the information gain, the more “useful” the attribute is considered to be.

Information Gain is a feature selection technique that is used to choose the best feature from a given dataset. Information Gain is based on the idea that the best feature is the one that gives the most information about the target class.

## What is entropy & information gain?

Entropy is a measure of randomness or uncertainty in a data set. The more entropy in a data set, the more randomness or uncertainty there is in the data. Information gain is a measure of how much information is gained by making a decision. If the entropy is less, information will be more. Information gain is used in decision trees and random forest to decide the best split.

The information gain is the difference in entropy before and after splitting a dataset. Given a probability distribution, the entropy before splitting is the sum of the probabilities of each data point. The entropy after splitting is the sum of the probabilities of each data point in each subset. The information gain is the difference between these two values.

### What is entropy & information gain?

The Entropy and Information Gain method focuses on purity and impurity in a node. The Gini Index or Impurity measures the probability for a random instance being misclassified when chosen randomly. The lower the Gini Index, the better the lower the likelihood of misclassification.

Information gain is the basic criterion used to decide whether a feature should be used to split a node or not. The feature with the optimal split, i.e. the highest value of information gain at a node of a decision tree, is used as the feature for splitting the node.

## What is entropy in data?

The entropy of a variable is a measure of the amount of information present in the variable. This amount is estimated based on the number of different values that are present in the variable, as well as the amount of surprise that this value of the variable holds.

The impurity of a node is the measure of how “mixed” the node is. A node is pure if all of its examples are of the same class. The entropy of a node is the measure of how “mixed” the node is. A node is pure if all of its examples are of the same class. The information gain of a node is the difference between the entropy of the node and the average entropy of its children. A higher information gain indicates a more “pure” node.

## What are the advantages of information gain?

Information gain is a useful metric for determining the order of attributes in the nodes of a decision tree. The main node is referred to as the parent node, whereas sub-nodes are known as child nodes. By using information gain, we can determine how good the splitting of nodes in a decision tree is. This metric is based on the principle that the attributes with the most information gain are the most useful for predicting the target class.

IG = 0 when there is only one class in the data. This is because we already know what the class is without having seen any attribute values.

### What is gini vs entropy vs information gain

Gini index and entropy are the criterion for calculating information gain. Decision tree algorithms use information gain to split a node. Both gini and entropy are measures of impurity of a node. A node having multiple classes is impure whereas a node having only one class is pure.

The Gini index is a way of measuring income inequality. It’s a single statistic that summarizes the dispersion of income across the entire income distribution. The Gini coefficient is used to calculate the Gini index.

## What is difference between Gini impurity and information gain?

Information gain is calculated by multiplying the probability of a class by the log base 2 of that class probability. This measures the amount of information that is gained by knowing the class membership of an instance. Gini impurity is calculated by subtracting the sum of the squared probabilities of each class from one. This measures the impurity of a set of instances, with a higher impurity indicating a more mixed set of instances.

One of the disadvantages of using Information Gain as the criterion for determining which feature to use as the root/next node is that it tends to prefer features with more unique values. This can be a problem if there are many features with a similar number of unique values, as it can lead to overfitting. Additionally, Information Gain can be biased if the dataset is not evenly distributed.

### Why is information gain biased

The information gain equation, G(T,X) is biased toward attributes that have a large number of values over attributes that have a smaller number of values. These ‘Super Attributes’ will easily be selected as the root, resulting in a broad tree that classifies perfectly but performs poorly on unseen instances.

Information Gain is a measure of the decrease in entropy (or disorder) of a system when given some information. In other words, it is a measure of how much information is required to reduce the entropy of a system.

Gain Ratio is a complement of Information Gain, devised to deal with its predecessor’s major problem. Gain Ratio overcomes the issue of Information Gain giving too much importance to attributes with a large number of values.

## Should information gain be high or low?

This is because information is simply a way to quantify how surprised we are by an event. If an event is very likely, then we’re not surprised by it at all and hence it has very little information. On the other hand, if an event is very unlikely, then we’re very surprised by it and hence it has a lot of information.

The entropy of a random variable is a measure of the amount of information that is needed to describe the variable. The higher the entropy, the more information that is needed. The entropy is also a measure of the unpredictability of the variable. A random variable with high entropy is more likely to be unpredictable than a random variable with low entropy.

### What is opposite of entropy

Negentropy refers to the tendency of a system to become more ordered over time. The opposite of entropy, negentropy represents a measure of a system’s organizational efficiency and health. In contrast to entropy, which is a measure of disorder, negentropy is a measure of order. While entropy measures the randomness or chaos within a system, negentropy measures the order and organization within the system.

One example of negentropy is the solar system. The planets within the solar system are constantly moving in an orderly fashion around the sun. The sun itself is also constantly giving off energy in a very ordered way. Another example of negentropy is the human body. The human body is made up of trillions of cells, all of which are working together in a very ordered way to keep the body functioning.

While entropy is a natural force that always eventually leads to disorder, negentropy is a force that can fight against entropy and maintain or even increase order. Negentropy is essential for the maintenance of all complex systems, including the solar system and the human body.

If an attribute can be used to make a unique classification for the result attribute, then the information gain is equal to the total entropy. This is because the attribute provides all of the information needed to make a prediction.

## To Sum Up

In data mining, information gain is a measure of the decrease in entropy (or uncertainity) of a target variable when a certain attribute is known.

Information gain is a data mining technique that helps identify important and relevant data. It does this by looking at the differences in entropy before and after the data is split on an attribute. Information gain can be used to identify which attributes are most relevant to the classification task and can also be used to improve the accuracy of classification models.