Gini index for ML (Performance measurement and many more..)

Motivation

You have developed machine learning model. What is next? You definitely want to check its performance.  Will checking accuracy be suffice? Might not be true for all cases. Consider the case where you want to capture credit card fraud. Your model may have high accuracy, but still it will not be good model. Why? Because it may not perform well in detecting credit card fraud.  

I am here talking about highly imbalanced dataset. Note that in total number of credit card history, most of them will be without any issue (Note:most credit card users behaves well ). In such case, a model may tend to have high bias. To detect it, we need different performance measurement methods.Gini index/coefficient is such measuring methods with its quite few exciting capabilities.

About Gini Index/Coefficient

1. The Gini coefficient measures the inequality among the values of a frequency distribution, such as levels of income. 
2. As a popular example, Gini coefficient is being used as measurement for household income inequality. More the inequality, higher the value
3.  Its value lies in the range [0,1].  Below pic gives glimpse of how the value changes

How is the Gini coefficient used in machine learning?

In machine learning, the Gini coefficient is often used as a metric for evaluating the performance of a model. The Gini coefficient is a measure of inequality, and it can be used to assess how well a model is able to correctly predict the labels of data points. The Gini coefficient ranges from 0 to 1, where 0 indicates perfect equality and 1 indicates perfect inequality. A high Gini coefficient indicates that the model is doing a good job of correctly predicting the labels of data points, while a low Gini coefficient indicates that the model is not doing a good job of correctly predicting the labels of data points

What are the benefits of using the Gini coefficient in machine learning?

The Gini coefficient is a widely used measure of inequality and is often used in machine learning to evaluate the performance of a model. The benefits of using the Gini coefficient in machine learning include its ability to provide a clear and concise measure of inequality, its ease of use, and its widely accepted nature.

How can the Gini coefficient be used to choose the right machine learning algorithm?

• The Gini coefficient can be used to compare different machine learning algorithms and to choose the best algorithm for a particular dataset. For example, if you have a dataset with a high Gini coefficient, you might want to choose an algorithm that is less sensitive to outliers, such as the k-nearest neighbours algorithm.
• You can also use the Gini coefficient to compare different datasets. For example, you might want to compare two datasets with different types of features (categorical vs. numerical) or different numbers of features (high-dimensional vs. low-dimensional). If the Gini coefficients are similar, then the datasets are likely to be similar in terms of their classification accuracy.

How can the Gini coefficient be used to improve machine learning models?

The Gini coefficient can be used in a number of ways to improve machine learning models, such as:

– As a criterion for splitting nodes in decision trees: A higher Gini means that the current group has high impurities therefore the split is more likely to be successful.

The default method used in sklearn is the gini index for the decision tree classifier.

– As a criterion for selecting features: A higher Gini for a feature means that it is more important for distinguishing between classes, and should be given greater weight.

– As a weighting factor in ensembles: When combining several models, those with higher Ginis should be given greater weight.

Caution while using

One potential problem is that it assumes that classes are equally important. In reality, however, some classes may be more important than others

Thanks to these helping hands

https://www.upgrad.com/blog/gini-index-for-decision-trees/

https://www.analyticsvidhya.com/blog/2021/03/how-to-select-best-split-in-decision-trees-gini-impurity/

https://analyticsindiamag.com/understanding-the-maths-behind-the-gini-impurity-method-for-decision-tree-split

https://youtu.be/BwSB__Ugo1s

https://www.analyticsvidhya.com/blog/2020/06/4-ways-split-decision-tree