Back to Lesson

Teacher Guide: Introduction to Regression

Learn how to find the best-fitting line through data points and make predictions using linear regression.

Present LessonShare to ClassroomView Student Page

Use this lesson with your class

Free, no student accounts needed.

Share with students

Students open the lesson and practise with instant feedback.

Printable worksheet

All practice problems on paper, with a separate answer key.

Worksheet Answer key

Class quiz

10 questions on Regression. Students join with a name, you see everyone's score.

For Teachers

Learning Objectives
  • Define linear regression and explain its purpose
  • Calculate the slope of a line from two points
  • Write the equation of a regression line in the form y=mx+by = mx + b
  • Use a regression equation to make predictions
  • Interpret the meaning of slope and y-intercept in real-world contexts
Prerequisites
  • • Understanding of coordinate planes and plotting points
  • • Ability to calculate slope using rise over run
  • • Familiarity with linear equations in slope-intercept form
  • • Basic understanding of scatter plots
Discussion Starters
  • 1. Why might predicting very far into the future using a regression line be unreliable?
  • 2. Can you think of two variables in your life that might have a linear relationship?
  • 3. What is the difference between correlation and causation? Give an example.
  • 4. How might businesses use regression to make decisions?
Common Misconceptions

The regression line must pass through every data point

Remediation: Show examples where points scatter around the line. Explain that the line minimizes total error, not individual errors.

A higher slope always means a better relationship

Remediation: Clarify that slope describes rate of change, not strength. A gentle slope with tight clustering is better than a steep slope with scattered points.

Differentiation Ideas

For Struggling Students:

  • • Start with data that perfectly fits a line before introducing scatter
  • • Use only positive slopes initially
  • • Provide slope formula reference cards
  • • Use concrete, relatable examples (height vs. shoe size)

For On-Level Students:

  • • Work with realistic scattered data
  • • Include negative slopes (inverse relationships)
  • • Practice both finding equations and making predictions
  • • Analyze the meaning of slope in context

For Advanced Students:

  • • Introduce the concept of residuals
  • • Discuss interpolation vs. extrapolation
  • • Connect to correlation coefficient (rr)
  • • Work with technology to fit regression lines to larger datasets
Standards Alignment
  • HSS.ID.B.6 (CCSS.MATH.CONTENT.HSS.ID.B.6)

    Represent data on two quantitative variables on a scatter plot, and describe how the variables are related

  • HSS.ID.B.6.C (CCSS.MATH.CONTENT.HSS.ID.B.6.C)

    Fit a linear function for a scatter plot that suggests a linear association

  • HSS.ID.C.7 (CCSS.MATH.CONTENT.HSS.ID.C.7)

    Interpret the slope and the intercept of a linear model in the context of the data

Lesson Resources
  • visualInteractive Regression Plotter

    Students plot points and see the line of best fit adjust automatically

  • activityReal Data Analysis

    Analyze real datasets and make predictions using regression

  • worksheetRegression Practice Problems

    Calculate slopes, find equations, and make predictions

Lesson Content

Everything students see: definition, examples, common mistakes, applications. Tap to open.

Definition

Linear regression is a statistical method used to find the straight line that best fits a set of data points. This line is called the line of best fit or regression line.
The equation of a regression line is:
y=mx+by = mx + b
where:
  • mm is the slope (how steep the line is)
  • bb is the y-intercept (where the line crosses the y-axis)
  • xx is the input variable (independent variable)
  • yy is the predicted output (dependent variable)
The goal of regression is to minimize the total distance between the data points and the line, allowing us to make predictions for new values of xx.

Worked Examples

A study shows that for every additional hour of studying, test scores increase by 5 points. If a student who studies 0 hours scores 50 points, what is the regression equation?
1

Identify the slope

Score increases by 5 points per hour of studying → m=5m = 5
2

Identify the y-intercept

When x=0x = 0 hours, the score is 50 points → b=50b = 50
3

Write the equation

Substitute m=5m = 5 and b=50b = 50 into y=mx+by = mx + b → y=5x+50y = 5x + 50

Common Mistakes

Confusing the order of subtraction in the slope formula

Why it's wrong: Using x2−x1y2−y1\frac{x_2 - x_1}{y_2 - y_1} instead of y2−y1x2−x1\frac{y_2 - y_1}{x_2 - x_1} gives the reciprocal of the correct slope.

Correct: Remember: slope is 'rise over run' - the change in yy (vertical) divided by the change in xx (horizontal).

Extrapolating too far beyond the data

Why it's wrong: The regression line is only reliable within the range of your data. Predicting far outside this range can lead to unrealistic results.

Correct: Be cautious about predictions for xx values much larger or smaller than your original data points.

Assuming correlation means causation

Why it's wrong: Just because two variables are related (correlated) does not mean one causes the other.

Correct: Regression shows relationships, but additional analysis is needed to establish causation.

Why It Matters

Linear regression is one of the most widely used tools in data science and statistics:
  • Business: Predicting sales based on advertising spending
  • Medicine: Estimating drug dosage based on patient weight
  • Economics: Forecasting GDP growth from various indicators
  • Sports: Projecting athlete performance from training metrics
  • Science: Modeling relationships between variables in experiments
Understanding regression helps you make data-driven decisions and predictions based on real evidence rather than guesswork.

Real World Applications

Predicting House Prices

Real estate analysts use regression to estimate home values based on factors like square footage, number of bedrooms, and location.

Example:

If homes sell for approximately 150 dollars per square foot with a base price of 50000 dollars, the equation might be y=150x+50000y = 150x + 50000, where xx is square footage.

1Try It Yourself

A real estate model shows: y=200x+30000y = 200x + 30000, where xx is square feet and yy is price in dollars.

What is the predicted price for a 1500 square foot home?

Step 1: Write the mathematical expression

Substitute x=1500x = 1500 into the equation:

Fuel Efficiency Analysis

Automotive engineers use regression to understand how car weight affects fuel consumption.

Example:

Data might show that fuel efficiency decreases by 0.005 km/L for every kilogram of additional weight.

2Try It Yourself

A car model shows: y=−0.01x+25y = -0.01x + 25, where xx is weight in kg and yy is fuel efficiency in km/L.

What efficiency is predicted for a car weighing 1200 kg?

Step 1: Write the mathematical expression

Calculate: y=−0.01(1200)+25y = -0.01(1200) + 25

Key Takeaways

  • 1Linear regression finds the straight line that best fits a set of data points
  • 2The regression equation is y=mx+by = mx + b, where mm is the slope and bb is the y-intercept
  • 3Slope is calculated as m=y2−y1x2−x1m = \frac{y_2 - y_1}{x_2 - x_1} (rise over run)
  • 4Once you have the equation, you can make predictions by substituting values for xx
  • 5Regression shows correlation, but correlation does not imply causation

Frequently Asked Questions

What if my data points do not fall exactly on a line?

Real data rarely falls perfectly on a line. The regression line minimizes the total squared distance from all points to the line. Some points will be above the line, some below - this is normal!

How do I know if my regression line is a good fit?

The R2R^2 value (coefficient of determination) measures how well the line fits. It ranges from 0 to 1 - higher values mean better fit. You will learn more about this in the lesson on correlation.

Can regression be used for non-linear relationships?

Linear regression only works for straight-line relationships. For curved relationships, you need polynomial regression or other advanced methods.

Glossary

Linear regression
A statistical method for finding the best-fitting straight line through data points
Line of best fit
The straight line that minimizes the distance between itself and all data points
Slope
The steepness of the line, representing the rate of change (mm in y=mx+by = mx + b)
Y-intercept
The point where the line crosses the y-axis (bb in y=mx+by = mx + b)
Prediction
Using the regression equation to estimate yy for a given value of xx
Independent variable
The input variable (xx) that we use to make predictions
Dependent variable
The output variable (yy) that we are trying to predict

More in This Topic

Linear Regression

Advanced25 min

Scatter Plots

Intermediate25 min

Line of Best Fit

Intermediate25 min

Making Predictions from Data

Intermediate25 min