What a Correlation Does Not Tell You

Lab Brief #7

🎯 Your mission

Understand the idea. Then look for it everywhere.

⚡ The twist

Nature loves to surprise the careful watcher.

What you'll learn

A strong correlation establishes that two variables move together. It says nothing about which one causes the other, whether a third variable drives both, or whether the relationship survives outside the range actually measured. Establishing cause requires either a controlled intervention or a mechanism demonstrated independently. The line of best fit drawn through a scatter graph is a description of the data, not an explanation of it, and extending it beyond the data is a guess.

Key words

correlation
A statistical relationship in which two variables change together, with no claim about cause.
confounding variable
A third factor influencing both variables and creating a false impression that one causes the other.

Make a hypothesis first

Before you start: write down what you think will happen, and why.

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "correlation" and "confounding variable" mean in your own words before you start.

Step 2 of 4 · Do

Plot ice cream sales against drowning incidents by month and describe the correlation. Then plot both against mean monthly temperature, and write which variable is the confounder and how the second pair of graphs demonstrates it.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 3

Ice cream sales correlate with drowning incidents because both are driven by:

How sure are you?😐 maybe

Question 2 of 3

Establishing a causal claim needs:

How sure are you?😐 maybe

Question 3 of 3

A line of best fit extended beyond the measured range is:

How sure are you?😐 maybe

Mind = blown

🔬 The more you look, the more nature shows you.

Nice work!

You got 0 of 3 right.

Next: Four Checks Before You Trust a Graph All lessons

🎯

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✨ More to explore

🌍 Where you see this in real life: This shows up in your everyday life more than you'd think.

🏆 Stretch challenge (try it this week): Try one experiment in real life this week — even a tiny one.

👨‍👩‍👧 For the dinner table: “What's the most surprising thing you learned today?”

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What a Correlation Does Not Tell You

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