Scatter Diagram: Definition & Examples

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  • 0:04 Visual Map of Your Data
  • 1:03 Creating a Scatter Diagram
  • 2:21 Scatter Diagram Example
  • 3:03 Lesson Summary
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Lesson Transcript
Instructor: Neelam Mehta

Neelam has taught variety of math and science subjects. She has masters' degrees in Chemical Engineering and Instructional Technology.

Scatter diagrams? What are those all about? Who uses them? Find out the answers to these questions and how scatter diagrams can be used to represent real world data.

Visual Map of Your Data

Let's meet Tom. Tom enjoys working in his vegetable garden. He loves all his vegetables, but the tomatoes are his favorite. Tom just wasn't happy with his tomato crop this year, so he decided to study tomatoes in his garden. He wants to know if there's any connection between the number of tomatoes on a plant and the hours of exposure to sun.

He brings out his lab notebook and starts to record the data. Tom counts the number of tomatoes on each plant. He also records the number of hours of sun each tomato plant gets during the day. Tom now takes the data back indoors and wonders how to make sense of it. Is there a connection between the two things that he measured?

That's where the scatter diagrams come in. Just like it sounds, a scatter diagram, or scatter plot, is a graph of your data. Scatter diagrams are types of graphs that help you find out if two things are connected. In math, we like to call those things variables. How do you know if there's a connection or a relationship between two variables? We measure the two variables and graph them on an (x, y) coordinate system.

Creating a Scatter Diagram

Let's return to Tom's tomato plants. Suppose this is the data that Tom collected.


Data Table for Tomato Plants


Let's plot this data on (x, y) coordinates. We'll plot the hours of exposure to sunlight on the x-axis and the number of tomatoes for the same plant on the y-axis.

Now we've plotted each point on the graph appearing below.


Scatter Diagram for Tomato Experiment


Notice that the number of tomatoes on a plant increases as the exposure to the sunlight increases. We can see this easily by drawing a trend line that best fits all your data points. Notice that the trend line is pointing in the northeast direction, which means it has a positive slope. This indicates that a positive relationship exists between the number of tomatoes on a plant and the hours of sunlight it receives.

Therefore, you can see that a scatter diagram is a graphical tool that helps us decide if two variables are related. Can we also have other types of relationships between two variables, or no relationship at all? Yes, absolutely.

A scatter diagram showing a negative relationship has a downward trend. In other words, the slope of the best-fit trend line is negative or pointing in the southeast direction, like in the image below.


Scatter Diagram with Negative Trend Line


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