Mosaic Plots (Topics 2.2-2.3)

Chapter 1 - Day 4

Learning Targets
  • Classify variables as categorical or quantitative.

  • Make and interpret bar graphs for categorical data.

  • Use bar graphs to compare distributions of categorical data.

  • Describe the nature of the association between two categorical variables.

Activity: What Will Be the Mascot?
Activity:
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Answer Key:
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The new College Board Course and Exam Description (CED) has provoked some anxiety amongst experienced AP Stats teachers. What is College Board going to change? What are they going to add? The quick answer is that they didn't change too much. But there is one change that threw us for a loop:

 

MOSAIC PLOTS!

 

We hope we weren't the only AP Stats teachers that had no clue what this meant. A quick Google search, and we think we have it sorted out. Start with a categorical variable, such as favorite math class, but for two different groups (East Kentwood Senior students and East Kentwood teachers). Make a segmented bar graph for each group. 

The segmented bar graph does well to inform us about the percent of each category within each group. The information that is missing is the size of each group. At East Kentwood, this sample included 100 Senior students and 20 teachers (we'll let you guess which two teachers picked AP Stats). These vastly different group sizes are not at all represented in the segmented bar graph. A mosaic plot allows us to see these group sizes by scaling on the x-axis!

We used the One Categorical Variable, Multiple Groups applet at www.stapplet.com to create the above mosaic plot.

Teaching Tip

Stats Medic to the rescue! (we hope). We have developed an all new lesson that you can use in your classroom. The context for this activity is about the school choosing a mascot, so you will likely want to download the Word document and make it specific for your school.

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