Information gain score: How it is calculated? Which factors are crucial?
Information gain is one of the most exciting ranking factors for modern search engines and so SEO. Many of Information Gain’s explanations have a lack of depth and missing approaches to optimizing information gain. This article schould give a deep overview about the concept, the calculation and SEO approaches to optimize for information gain. Also the connection to phrase based indexing is explained.
This inisghts about information gain are based on fundamental knowledge of the most interesting Google patents about information gain.
What is information gain in context of information retrieval and search engines?
Information gain refers to a score that indicates the additional information included in a document beyond the information contained in documents previously viewed by a user. This score helps in determining how much new information a document will provide to the user compared to what the user has already seen.
Techniques involve data from documents being applied across a machine learning model to generate an information gain score, assisting in presenting documents to the user in a manner that prioritizes those with higher scores of new information.
In information retrieval and search engines, information gain is used to evaluate the relevance and effectiveness of documents or terms in reducing uncertainty about the information needs of users. It helps in ranking documents and enhancing the overall search experience.
Entropy is a measure of uncertainty or randomness in a set of outcomes. In the context of information theory, it quantifies the amount of information needed to describe the state of a system.
A larger information gain suggests a lower entropy group or groups of samples, and hence less surprise.

What is the role of entropy in information gain?
Entropy plays a crucial role in information gain within decision tree learning. Specifically, entropy is a measure of impurity or uncertainty in a dataset. When constructing decision trees, information gain is used to determine which attribute best separates the data into distinct classes. Information gain is calculated as the reduction in entropy that results from partitioning the data based on a given attribute.
- Entropy: Measures impurity or randomness in data.
- High entropy: Data is very mixed and classes are unevenly spread out.
- Low entropy: Data is more uniform and classes are evenly spread out.
- Maximum entropy values change with the number of classes (e.g., 2 classes: max entropy is 1, 4 classes: max entropy is 2).
The process of determining an information score
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