Create and Analyze Scatter Plots

A set of bivariate data involves two variables. Bivariate data are used to explore the relationship between two variables. You can graph bivariate data on a scatter plot. A scatter plot is a graph with points plotted to show the relationship between two sets of data.

Example

After gather data showing the number of pages in some of the library books and the price of the books, Kayce made a table that displayed this information. She used pages as the X value and price as the Y value. The data can be plotted on a graph as a scatter plot. (Do not connect the dots.)

Table and graph illustrating pages and price

Rae wanted to see if there was a relationship between those who watched television and spent doing outside activities. She surveyed her friends and made a table of the information. Then, she plotted this information on a graph as a scatter plot.

Table and graph illustrating tv hours and outside hours

If one variable tends to increase, there is a positive correlation between the two sets of data; if one variable tends to decrease, a negative correlation would exist. If the plot on the graph is scattered in such a way that it does not approximate a line, there is no correlation between the sets of data.

Example

five graphs showing different correlations

Line of Best Fit

You can graph a line on a scatter plot that can help demonstrate the relationship in the data set. This line is also called a trend line because it shows how the data is trending. When you draw a line of best fit, or trend line. in your graph, you can easily make predictions based on your data.

To create a line of best fit, draw a line through the middle of your data points. Try to keep about the same number of points above and below your line. Your line may or may not go through any of the points from the data.

Drawing a Trend Line Video

Try It

The scatter plot shows a relationship between the amount of money collected at the concession Stand and the number of tickets sold at a Cinema. Use the scatterplot trend line to predict how much money will be collected at the concession stand when 200 tickets have been sold.

Concession stand sales graph

Did you predict $750.00? Great job!

Scatter Plots and Trend Lines Practice

If you would like to practice more problems and check your work, click here. Make sure you check your answers and look at the course resources or ask your teacher if there are any problems you do not understand.

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