What is Regression Line – Formula, Calculation, Example, Application

What is Regression Line – Formula, Calculation, Example, Application

7 mins read160 Views Comment
Atul Harsha
Senior Manager Content
Updated on Oct 12, 2023 09:28 IST

The regression line represents the best estimate of one variable based on the value of another, capturing the average relationship between them. In simple terms, the regression line is like a guide that shows us the general trend between two things.


Imagine you’ve just launched a brand-new type of sneaker on an online store. Every day, you run ads on social media platforms like Instagram and YouTube to promote your sneakers. You’ve noticed something interesting: The trend was – the more ads you run, the more sneakers you sell!

Introducing the Idea of a Trend

Think about it like this: the more often people see something, the more likely they are to buy it, right? So, if we were to draw this on a graph, with the number of ads on the bottom (X-axis) and the number of sneakers sold on the side (Y-axis), we’d see a line going up. This line which shows us the relationship between the number of ads and sales is the regression line.

What is a Regression Line?

A regression line or line of regression is a straight line that best represents the relationship between two sets of data. By understanding this relationship, businesses and researchers can make better decisions and forecasts.

For example, on an e-platform selling sneakers, if we chart the number of online ads against the number of sneakers sold, the regression line will indicate how, on average, sales might increase with each additional ad. It’s like drawing a line of best fit through our data points to predict how many sneakers we might sell based on our advertising efforts.

Drawing the Regression Line

On a graph paper or whiteboard, draw a scatter plot with some points representing the number of ads and the number of sneakers sold. Then draw a line that seems to fit the points best.


This line is our magic predictor! It helps us guess “How many sneakers we might sell if we run a certain number of ads.

Read More: How to perform Regression Analysis?

Linear Regression in Machine Learning
Linear Regression in Machine Learning
Linear regression in machine learning helps you find out patterns and relationships in data and make an educated decision or prediction. The article discusses linear regression in ML to model...read more
Difference Between Linear Regression and Logistic Regression
Difference Between Linear Regression and Logistic Regression
Linear Regression and Logistic Regression are both Supervised Machine Learning models that make use of labelled datasets to make predictions. However, there’s a fundamental difference in their usage – Linear...read more
Least Square Regression in Machine Learning
Least Square Regression in Machine Learning
This article discusses the concept of linear regression. We have also covered least square regression in machine learning. Let’s begin! The article covers the concept of Least Square Regression...read more

Why use Regression Line?

Using a regression line provides clarity, direction, and a data-driven approach to various challenges and questions across different fields. It helps with the following:

  • Predictive Insights: Helps forecast future values based on historical data.
  • Decision Making: Assists businesses in making informed decisions, such as budget allocation or inventory planning.
  • Understanding Relationships: Reveals the nature and strength of the relationship between variables.
  • Optimizing Strategies: Enables fine-tuning of strategies, like marketing campaigns, based on predicted outcomes.
  • Resource Allocation: Guides where resources (like money or time) can be most effectively spent.
  • Risk Management: Helps in assessing risks and uncertainties in various scenarios.
  • Cost Efficiency: By predicting outcomes, businesses can avoid unnecessary expenses.
  • Performance Evaluation: Allows for the assessment of the effectiveness of interventions or changes made in a system.

Introducing the Formula

The line can be described with a simple formula:

Sneakers Sold = (Number of ads × Sales boost) + Base Sales

  • Sales boost is how much our sales increase for each ad, on average.
  • Base Sales are the sales we make even without any ads, maybe from people who just stumble upon our website.

Simple Calculation Example:

Let’s say for every ad we run, we sell 5 more sneakers, and we have a base sale of 10 sneakers even without ads. If we run 20 ads today, how many sneakers can we expect to sell?

Using the formula: Sneakers Sold = (20 ads × 5 sneakers/ad) + 10 sneakers = 110 sneakers.

So, by running 20 ads, we can predict we’ll sell 110 sneakers!

Read More: Understanding and implementing Linear Regression formula in depth

Making it Exciting:

Now, here’s the thrilling part: Imagine if we could perfectly predict our sales just by deciding how many ads to run! We could plan special offers, stock up our inventory, and even set goals for our business. This prediction line, or regression line as the experts call it, is like having a crystal ball for our sneaker business!

Guess the Sales! Game:

Before we dive deeper, let’s play a quick game. Here are three days where we ran 10, 15, and 25 ads respectively. Based on our previous discussion, can you guess how many sneakers we sold on each of those days? Write down your predictions!

Learn More: Compare and get certified with best Regression Course in the market

Real-World Implications

  • Budgeting and Planning: Knowing how ads affect sales isn’t just cool—it’s crucial for our business. If we know that every ad brings in sales of 5 sneakers, and each sneaker gives us a profit of $10, then we can calculate how much profit we’ll make for each ad. This helps us decide our advertising budget. Too few ads, and we miss out on sales. Too many, and we might be wasting money.
  • Stock Management: Imagine the chaos if 500 people ordered our sneakers, but we only had 100 in stock! Or the opposite, where we stock up 500 sneakers, but only 10 get sold. Using our regression line, we can predict sales and manage our stock better.

Fun Facts related to Regression

Topic Fun Fact
Big Screen Predictions Hollywood uses regression to predict box office hits, considering factors like star actors, directors, and movie release dates.
Music to Your Ears Spotify’s song recommendations for you? They’re powered by regression models analyzing your listening habits.
Sports Analytics Regression is a MVP in sports for predicting player performance, game outcomes, and even ticket sales.
Weather Wonders Meteorologists use regression to help forecast the weather, analyzing patterns like cloud formations and rainfall.
E-Commerce Magic Amazon’s “recommended for you” section is not magic, but regression, predicting what you might want to buy next.
Pricey Paintings Art auction houses use regression to estimate painting sales prices, considering the artist, painting size, and colors used.
Coffee Craze Starbucks uses regression to pick new store locations, analyzing local population, competitors, and traffic patterns.
Space Exploration NASA relies on regression to predict equipment performance for space missions, ensuring rovers can handle Mars’ terrain.
Video Game Victory Game developers adjust game difficulty using regression, analyzing player performance to tweak challenges.

Historical Origin of Regression

The term ‘regression’ originated from Sir Francis Galton’s study on heredity. While examining the heights of parents and their children, he observed that although children of tall parents tended to be tall themselves, their heights often “regressed” towards the average height of the population. Thus, he named this phenomenon “regression to the mean.”

Potential Challenges and Limitations of using Regression Line

Limitation/Challenge Explanation
Overfitting If our regression model is too complex, it might fit our past sales data perfectly but fail to predict future sales accurately. This is like tailoring a shirt so precisely to past measurements that it doesn’t fit when you wear it next time.
External Factors Events like a celebrity endorsement, a viral social media post, or even global events (like a pandemic) can affect sneaker sales but might not be accounted for in the regression model.
Non-linear Relationships The relationship between ads and sales might not always be linear. After a certain point, more ads might not lead to a proportional increase in sales. This is similar to pouring water into a glass; it fills up linearly until it overflows.
Multicollinearity Other factors, like the quality of the ads, time of year, or introduction of new sneaker designs, can influence sales. If these factors are correlated with the number of ads, it can distort the regression results.
Data Quality If the data on past ads and sales is inaccurate or incomplete, the regression model’s predictions will be off. It’s the classic case of “garbage in, garbage out.”
Assumption Violations Regression makes several assumptions, like constant variance and normally distributed errors. If these are violated, our predictions can be misleading.
Saturation Point There might be a saturation point where running more ads doesn’t significantly boost sales, as the audience becomes “immune” to the ads or the market gets saturated.
Temporal Factors Sales might be influenced by temporal factors like holidays, seasons, or school years. If the regression model doesn’t account for these, it might miss seasonal sales spikes.
Ad Fatigue If the same ad is shown too frequently, potential customers might get tired of it, leading to decreased effectiveness over time.

Conclusion with a Thought-Provoking Question

Regression helps us make informed decisions, but it’s also essential to stay flexible and adapt to changes. With the power of prediction, we can plan, strategize, and grow our business. It lets us peek into the future and make smart decisions today. Whether it’s sneakers, concert tickets, or even ice creams on a hot day, understanding trends can be a game-changer!” But here’s a question for you: If you had this predictive power, how would you use it in your daily life or future business?

Learn More: Get enrolled into Logistic Regression Course

Read More on Regression:

How to Improve the Accuracy of Regression Model?
How to Improve the Accuracy of Regression Model?
In this article, we will discuss how to improve accuracy of regression model with the help of simple examples to understand the concepts.
Cost function in linear regression
Cost function in linear regression
This article revolves around cost function in machine learning and covered different types of cost function.
Difference Between Linear and Multiple Regression
Difference Between Linear and Multiple Regression
Linear regression examines the relationship between one predictor and an outcome, while multiple regression delves into how several predictors influence that outcome. Both are essential tools in predictive analytics, but...read more
Regression Testing – All That You Need To Know
Regression Testing – All That You Need To Know
Even minor changes can have disastrous results when software developers change or modify their code. As a result, testing, or in particular Regression Testing, becomes essential because a buggy application with...read more
Assumptions of Linear Regression
Assumptions of Linear Regression
There are certain assumptions of linear regression algorithm that must be satisfied before implementing over any model, otherwise it will lead to insignificant result.
Multiple linear regression
Multiple linear regression
Multiple linear regression refers to a statistical technique that is used to predict the outcome of a variable based on the value of two or more variables. In this article...read more
Most Popular Regression in Machine Learning Techniques
Most Popular Regression in Machine Learning Techniques
Regression in machine learning is a subfield of supervised machine learning aimed to establish a relationship between different quantitative variables by formulating mathematical equations. Some of the uses are the...read more
How to Calculate R squared in Linear Regression
How to Calculate R squared in Linear Regression
In this article we focussed on R-squared in Linear Regression in which explain the procedure of calculating R squared value in step by step way and with example.
Ridge Regression vs Lasso Regression
Ridge Regression vs Lasso Regression
Regularization techniques (like Lasso and ridge regression) are used to enhance the performance and interpretability of the machine-learning model, especially in situations where the traditional linear regression method fails. Lasso...read more
About the Author
Atul Harsha
Senior Manager Content

Experienced AI and Machine Learning content creator with a passion for using data to solve real-world challenges. I specialize in Python, SQL, NLP, and Data Visualization. My goal is to make data science engaging an... Read Full Bio