Introduction to Box Plots

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Objective

SWBAT: • Identify and label the minimum, maximum, lower quartile, upper quartile, and mean of a data set and box plot. • Analyze and compare box plots.

Big Idea

What is a box plot? What are quartiles? Students learn about the different parts of a box plot and analyze their information.

Do Now

7 minutes

See my Do Now in my Strategy folder that explains my beginning of class routines.

Often, I create do nows that have problems that connect to the task that students will be working on that day.  Today I want students to analyze a circle graph in order to answer questions. Each edition of Scholastic Action  typically includes a graph on its back page.

I ask for students to share their thinking.  Students are engaging in MP3: Construct viable arguments and critique the reasoning of others.

Problem

7 minutes

I introduce the problem to students.  I want students to apply what they already know minimum, maximum, and median to analyze the box plot.  Students participate in a Think Write Pair Share.  I walk around and monitor student progress as they work.

I call on students to share out their ideas.  I push students to support their idea with data from the set.  I am interested to see what students think about the dots at 28 and 39.  Students are engaged in MP3: Construct viable arguments and critique the reasoning of others and MP2: Reason abstractly and quantitatively

Box Plots

6 minutes

I reveal the name and definition of each part of the box plot.  I show students that finding the lower quartile and upper quartile is just finding the median of a different part of the data set.  I want students to see the connection between how each part is identified in the data set and then translated to the box plot.  

Percent of Data

7 minutes

I have students participate in a Think Write Pair Share.  Students are engaging in MP3: Construct viable arguments and critique the reasoning of others.  I want students to make a connection between what they know about the median and the percent of data.  If students understand that a median splits the data set down the middle, they should understand that 50% of the data is before the median and 50% of the data is after the median.  Students can use the same reasoning to determine that 25% of the data is between the minimum and the lower quartile. 

I call on students to share out their observations.  If students are struggling, I may ask one or more of the following questions:

  • How fraction of the data is before the median?  After?
  • How can we express that as a percent?
  • What does the upper quartile represent?
  • What percent must be after the upper quartile?

I want students to share out what they think the word quartile means.  If students are struggling, I write these words on the board: quart, quarter, and quartet.  I ask students to think about what the word part “quart” means in each word.  I want students to see that quart- connects to four.  There are four quarts in a gallon, four quarters in a dollar, and four people in a quartet.  If we break our data into quartiles, we are breaking it up into four parts.  This means that each quartile represents ¼ or 25% of the data in the data set.

Analyzing Box Plots

13 minutes

Note:

  • Before this lesson I create and Post a Key.

I explain to students that they will be working to analyze the box plots.   I ask students what they can do if they get stuck.  I want students to realize that they can check their notes and check in with their partner if they are stuck, before asking me a question.

As students work, I walk around and monitor student progress and behavior.  If students complete a page, I quickly scan their work.  If they are on track, I send them to check their work with the key.  If students are struggling, I may ask them one of the following questions:

  • What is the question asking?
  • What is does this part of the box plot tell us?  Where can we find it? 
  • What did our notes say?
  • What does a quartile represent? 

If students complete the questions they can work on the challenge problems.

Closure and Ticket to Go

10 minutes

I ask students to flip to the closure problem.  I ask students how the age of the players on the Houston Rockets compares to the age of the players on the Chicago Bulls.  I explain that they need to write 5 observations by analyzing the box plots.  They can use the questions at the bottom to help them if they are stuck.

Students participate in a Think Pair Share.  Students are engaging in MP1: Make sense of problems and persevere in solving them and MP3: Construct a viable argument and critique the reasoning of others

I call on students to share out their observations.  I push students to use accurate language and to use the box plot to support their observation.  Students are engaging in MP6: Attend to precision

I pass out the Ticket to Go and the Homework.