Difference between Regression and Classification Algorithms

Classification and regression are the very basic and important topics in machine learning. The article covers the major differences between Regression and Classification algorithms in machine learning.

When you have just started delving into Machine Learning, differentiating between Regression and Classification algorithms can be a bit confusing. Implementing the correct methodology while solving ML problems is the key to making accurate predictions.

Both are Supervised Learning Algorithms that use labeled data (aka training datasets) to train models to predict accurate outcomes.

If we represent the predicted output by ‘y‘ and the input data as ‘x‘, then supervised algorithms are employed to estimate the mapping function ‘f‘, such that y = f(x). 

However, there’s a fundamental difference in their usage – the Classification algorithms basically predict a categorical outcome, and Regression algorithms are used to predict a numerical outcome. 

In this blog, we will cover the following sections:

• Defining Regression Problems
• How Does a Regression Algorithm Work?
• Types of Regression Algorithms
• Defining Classification Problems
• How Does a Classification Algorithm Work?
• Types of Classification Algorithms
• Regression Vs. Classification Comparison Table
• Endnotes

Defining Regression Problems

Regression is a technique that predicts the continuous quantity outcome variable based on the independent variable(s). 

Few more examples of regression problems –

• Price of a liter of petrol
• Value of a stock
• The popularity of a newly released album
• Sales revenue generated by a business

How Does a Regression Algorithm Work?

Regression algorithms attempt to approximate the mapping function ‘f‘ based on the existing input data such that when new data ‘x‘ is fed to the model, the numerical or continuous output ‘y‘ can be predicted as accurately as possible.

When dealing with regression problems, commonly linear, our goal is to find the best fit line for our data such that the equation y = f(x) becomes linear, i.e.,

Let’s understand this through a fun little example – a company wants to predict the salary a person would draw based on the years of experience.

As the years of experience (x) increase, so does the salary (y). We can plot the known data for better visual understanding:

Our goal is to find a straight line, called the regression line, that best fits our plot. We can do this by finding the slope and intercept of this line. These values are actually the regression coefficients. With these values, our regression model will help predict the future salaries of employees based on their years of experience. 

In the above example, we’re considering only one input variable (x), that is, the years of experience. However, there can be multiple factors affecting employee salaries. This would then become a multi-linear regression problem with many input variables (xᵢ). 

Regression algorithms can be of non-linear types as well. Such algorithms model a non-linear relationship between the dependent (output) and independent (input) variables. They are used when the data shows a curvy trend.

Types of Regression Algorithms

Common regression algorithms include:

• Simple Linear Regression
• Multiple Linear Regression
• Polynomial Regression
• Support Vector Regression (SVR)
• Decision Tree Regression
• Random Forest Regression

Defining Classification Problems

Classification is a technique that predicts the discrete class label output to which the data element belongs.

Few more examples of classification problems –

• Spam texts/e-mails
• Segregation of waste 
• Cancer detection
• Churn Prediction

How Does a Classification Algorithm Work?

Classification algorithms attempt to approximate the mapping function ‘f’ basis the existing input data such that when new data ‘x’ is fed to the model, we can predict the categorical or discrete output ‘y’ as accurately as possible.

Let’s understand this through a fun little example – Your friend has a high fever, and the doctor wants to run some tests to determine what disease he might have.

A classification model can be used for such medical diagnoses. One can build a Disease Classifier Model that considers the patient’s temperature and health records to predict whether this person has flu, pneumonia, or some other disease.

When training a classifier on a known dataset, you define a set of hyper-planes, called decision boundary, that separates the data points into specific classes, where the classification algorithm switches from one category to another. 

For example, on one side of the decision boundary, data points are more likely to be called class A (or Disease A). While on the other side of the boundary, data points can be called class B (or Disease B). We use Binary Classifiers in case there are only two classes and Multi-class Classifiers for more than two class divisions.

Types of Classification Algorithms

Common classification algorithms include:

• Logistic Regression 
• K-Nearest Neighbours
• Support Vector Machines
• Kernel SVM
• Naïve Bayes
• Decision Tree Classification
• Random Forest Classification

Note that, though the name is Logistic “Regression” it is actually a classification algorithm.

Regression Vs. Classification Comparison Table

Endnotes

Regression and Classification algorithms are instrumental in solving Machine Learning problems. Hence, a clear understanding of choosing the correct model that deploys the best possible solution is necessary. Artificial Intelligence & Machine Learning is an increasingly growing domain that has hugely impacted big businesses worldwide. Interested in being a part of this frenzy? Explore related articles here.

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