The Big Picture: What Are We Even Measuring?

Just keep in mind the following questions:

1. “Are these two things related?” – This is where correlation comes in.
2. “If I change one thing, how much does the other thing change?” – This is where regression comes in.

Correlation Coefficient: The Relationship Detective

The correlation coefficient (usually represented as ‘r’) tells us whether two variables move together and how strongly they’re associated.

What It Measures

Correlation measures the strength and direction of a linear relationship between two variables. It answers: “Do these variables tend to increase or decrease together?”

The Scale

The value always falls between -1 and +1:

• +1: Perfect positive correlation (as one goes up, the other goes up perfectly)
• 0: No linear relationship (they’re doing their own thing)
• -1: Perfect negative correlation (as one goes up, the other goes down perfectly)

What correlation does not tell.

And here’s the crucial part: correlation doesn’t tell you how much one variable changes when the other changes. It just says they move together.

It’s not about the units or the actual change it’s about the pattern.

Regression Coefficient: The Prediction Machine

Regression coefficients (often represented as ‘b’ ie beta) is a different thing entirely. Here we’re talking about prediction and quantifying change.

What It Measures

A regression coefficient tells you how much the dependent variable (the outcome) changes when the independent variable (the predictor) changes by one unit, while holding everything else constant.

The Scale

Regression coefficients are NOT standardized. They’re in the units of your variables!

This means they can be any value: 0.5, 50, -200, whatever makes sense for your data.

What It DOES Tell You

Regression coefficients give you a formula to predict outcomes. If you have the equation:

y = mx + c

You can plug in any x and estimate y.

The Key Differences at a Glance

1. Purpose

• Correlation: Describes the strength of association
• Regression: Predicts and quantifies change

2. Units

• Correlation: No units! It’s standardized (always between -1 and +1)
• Regression: Has units! Depends on what you’re measuring

3. Symmetry

• Correlation: Symmetric (correlation between X and Y equals correlation between Y and X)
• Regression: Asymmetric (regressing Y on X is different from regressing X on Y)

4. What They Tell You

• Correlation: “These variables move together with this strength”
• Regression: “When X increases by 1, Y changes by this amount”

When to Use Which?

Use correlation when:

• You want to know if two things are related
• You’re exploring data and looking for patterns
• You want to compare relationship strengths across different variable pairs
• You don’t have a clear cause-effect hypothesis

Use regression when:

• You want to predict outcomes
• You need to know the magnitude of change
• You’re testing specific hypotheses about how variables affect each other
• You want to control for multiple variables at once

The Connection Between Them

Note that in simple linear regression (with just one predictor), correlation and regression are mathematically related! The standardized regression coefficient (called beta in some contexts) actually equals the correlation coefficient. But in their raw forms, they’re giving you different information.

Hope you’ve understood dear reader and leave a comment if you have any concern