A scatter plot puts one point for each thing measured, using two measurements as coordinates.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Reading the cloud
If the points rise to the right the association is positive. If they fall, it is negative.
Fitting a line
A straight line drawn through the middle of the cloud can be used to make predictions.
Association is not cause
Two things rising together does not prove one causes the other.
Two measurements from each subject
A scatter plot records two values for each individual — height and arm span, say — as a single point. It shows how the two vary together, which a single-variable display cannot.
Positive, negative, or none
If y tends to rise as x rises, the association is positive. If y falls as x rises, it is negative. If the points show no trend, there is no association. The word "tends" matters — associations are about the overall pattern, not every point.
Strength and form
A tight band of points means a strong association; a wide cloud means a weak one. The pattern may also be curved rather than linear. Describing form, direction and strength together is a complete description of a scatter plot.
Association is not causation
Ice cream sales and drowning deaths rise together, but neither causes the other — hot weather causes both. A scatter plot can show that two things move together; it can never show that one makes the other happen.
Step 2: Try It Yourself
Tap and try it out.
The slope is 1: for every 1 across, the line goes 1 up.
Step 3: Watch an Example
One step at a time.
Watch Ana Read a Scatter Plot
Ana looks at hours studied against test score.
- Step 1
She sees the points generally rise to the right.
Step 4: Your Turn
Practice makes it stick.
The Direction
Problem 1 of 2
Points fall to the right. What kind of association is that?
The Prediction
Problem 2 of 2
A fitted line is y = 2x + 1. What does it predict when x = 4?
Read the Cloud
1 of 4
Points rise to the right. Positive or negative?
2 of 4
Fitted line y = 3x + 2. Predict for x = 5.
3 of 4
Fitted line y = x + 4. Predict for x = 6.
4 of 4
Does association prove cause?
Step 5: Quick Check
Show what you know.
Question 1 of 2
Fitted line y = 2x + 3. Predict for x = 6.
Question 2 of 2
What does a negative association look like?
What You Learned
- A scatter plot shows two measurements from each thing.
- Rising to the right is positive association, falling is negative.
- A fitted line predicts, but association is not cause.