Majority class

See also: Machine learning terms

Introduction

In machine learning, the majority class is the more common label in a dataset that is imbalanced. For example, in a dataset where there are 80% "yes" and 20% "no", "yes" is the majority class. The opposite of the majority class the minority class.

Impact on Model Performance

A majority class in a dataset can have an enormous effect on the performance of a machine learning model. This occurs because the model may be biased towards predicting the majority class even when there is more importance placed on a minority one for solving specific problems - this bias is known as class imbalance and may lead to suboptimal performance if not addressed properly.

Class imbalance can be addressed using various techniques, such as oversampling the minority class, undersampling the majority class or using both together. Another approach relies on weighting; where misclassifying instances from one group at a higher cost than misclassifying from another. This can be accomplished either through cost-sensitive learning algorithms or altering the loss function used during training.

Examples of Majority Class in Machine Learning

One common application of machine learning to medical diagnosis involves the majority class: "healthy." On the other hand, if a minority patient is classified as "ill," accurately predicting them can have serious repercussions. To accurately predict which class belongs where, misclassifying an ill patient as healthy can have devastating results.

Another example is fraud detection, where the majority class might be "not fraud" and the minority "fraud." To accurately predict this minority class, as misclassifying a fraudulent transaction as not fraud can cause substantial financial losses.

Explain Like I'm 5 (ELI5)

In machine learning, the majority class is analogous to the most popular answer on a class test. If there are 10 questions and 9 of them are about one thing, that answer becomes the majority class. When the computer tries to figure out an answer, it might be easier for it to just pick the most popular answer even if it's incorrect. But sometimes these less popular answers are necessary too - like when determining if someone is sick or not. In order to help the computer pick the correct response, people use special tricks in order to make it pay more attention towards these less popular responses.

Explain Like I'm 5 (ELI5)

Imagine having a large basket filled with various colored candies - red, green, blue, yellow and so on. In this situation the majority class would be determined by which candy color there is the majority of in the basket.

Machine learning relies on the concept of the majority class, which refers to the class that occurs most often within a dataset. Just like in the candy example, this machine learning model seeks out the class that occurs most frequently and uses that data to make predictions about new data sets.

Imagine trying to guess the color of candy inside a closed bag without looking. If most of the candies in the basket are red, you might assume that whatever's inside will also be red. That's how a machine learning model can use data from a majority class to make predictions!

Definition

A majority class is the one with the greatest number of instances or data points in a dataset. When two classes are present, this means the majority class will have more instances than its rival. Similarly, in multi-class classification problems, the majority class would be determined by which class has generated more instances compared to all others.

Importance

Understanding the majority class in machine learning is crucial, as it directly affects the model's performance. When a dataset is imbalanced, meaning one class has significantly more instances than all others, the model may perform poorly on that minority class due to dominance of that majority in decision-making processes. As a result, biased results may arise.

Imbalanced Data

Imbalanced data refers to a situation in which the number of instances belonging to one class is significantly larger than all others. For instance, when dealing with credit card transactions, fraudulent transactions may be rarer compared to genuine ones; thus, majority of transactions would be genuine while minority are fraudulent ones.

When training a machine learning model on imbalanced data, the model often becomes biased towards the majority class. This occurs because the model is designed to maximize its accuracy by correctly classifying the majority. As such, the model may neglect or misclassify the minority population, leading to subpar performance.

Solutions

There are various techniques that can be employed to address the issue of imbalanced data. One approach is oversampling the minority class, creating more instances from that population; this method is known as oversampling. Conversely, undersampling the majority class by decreasing its number of instances is known as undersampling.

Other techniques involve cost-sensitive learning algorithms, where misclassifying minorities is more costly than misclassifying majority classes. Furthermore, ensemble methods can be employed, where multiple models are trained and combined together for improved performance.

Explain Like I'm 5 (ELI5)

Machine learning often requires categorising objects into distinct classes. The majority class is the one with the most members; for instance, if an animal group includes 10 dogs and 2 cats, then that would constitute its majority class.

Sometimes, we might have more of one thing than another, making it difficult for a computer to learn how to classify them correctly. This situation is known as imbalanced data. To aid the machine in learning better, we employ different tricks like making more copies of what we don't have much of and paying more attention to that which is scarce.

Explain Like I'm 5 (ELI5)

Imagine playing a game with your friends where the objective is to guess the color of each toy. You have many toys, most of them blue but some red. Which color do you guess first?

Let's say your friend always guesses the toy is blue, no matter what. They won't even look at it to determine whether it really is blue or red.

Machine learning refers to this friend's guess as the "majority class". After all, most toys are blue; thus, guessing blue would be what most people would do if presented with this choice.

Similar to machine learning, when trying to predict something, we might have access to a great deal of data that indicates one thing is more common than another. So we can make an educated guess similar to your friend's guess and say that our target is "majority class".

Sometimes the minority class may actually be our best bet; nonetheless, it can serve as a good place to begin.