Scatter Plot

Sommaire

In short: A scatter plot is a graph that shows paired data as dots on a coordinate grid, so you can see whether and how two quantities are related.

8th GradeStatistics8.SP.A.1

What is Scatter Plot?

Each dot on a scatter plot stands for one case with two measurements, for example a student’s hours of study and the test score. The horizontal position shows one value and the vertical position shows the other.

The overall shape of the cloud of dots reveals the association. Dots drifting upward suggest a positive association, dots drifting downward a negative one, and a shapeless cloud no association. A curved cloud means the link is nonlinear, and a dot far from the rest is an outlier.

How to spot it

A table lists two numbers for each person, object or day, and the question asks if they are connected.
You see dots on a grid instead of a connected line or bars.
The wording asks about trend, association, clusters, gaps or outliers.
A prediction is requested from a pattern in measured data.

The method

Choose which variable goes on the horizontal axis and which on the vertical, then label both with units.
Plot each pair \((x, y)\) as a single dot.
Describe the pattern: direction (positive, negative, none), shape (linear or curved) and strength (tight or loose).
Point out any outlier and any cluster before drawing conclusions.

Eight students: more hours of study goes with higher scores.

Scatter Plot: solved example

Problem

A lemonade stand records the afternoon temperature (°F) and cups sold: \((68, 14)\), \((72, 19)\), \((75, 22)\), \((81, 31)\), \((85, 35)\), \((90, 41)\). Describe the association.

Solution

Plot the points with temperature on the horizontal axis. As temperature increases, cups sold increase, and the dots sit close to a rising straight band, so there is a strong positive linear association.

No point is far from the rest, so there are no outliers. From 68°F to 90°F, a gain of 22 degrees, sales rose by 27 cups, about 1.2 more cups per degree.

Try it

Question 1

A plot of car age against resale value shows dots sloping down from left to right. What kind of association is that?

Show the answer

Negative: as age increases, value decreases.

Question 2

The dots of a plot form a U-shaped curve. Is the association linear?

Show the answer

No. The pattern is curved, so the association is nonlinear.

Scatter Plot vs. Histogram

A histogram shows one variable, grouped into bars that count how many values fall in each interval. A scatter plot shows two variables at once, with one dot per case, and is built to reveal a relationship between them rather than the spread of a single list.

Histogram

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Whole dictionary: A–Z · 8th Grade · Statistics

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