Dispersion of Data (Day 2 0f 2)

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SWBAT find and describe the dispersion of a set of data about military salaries.

Big Idea

To check the work of variance and standard deviation using a calculator, and be able to support the description with the math.

Partner Work

25 minutes

This is the second day of a two-day lesson, so students continue working on thePartner Activity that I assigned the previous day.  I assigned students to work with their table partner with a set of data about military salaries.  Students are to work by hand to find and describe the spread of the data using:

1.  Range

2.  Interquartile Range

3.  Outliers/Gaps

4.  Variance

5.  Standard Deviation

Students are to do all of the calculations by hand.  They may use the Graphing Calculator for arithmetic operations like squaring, however they are to do the other calculations by hand. Students are to write out the formulas and show all of their work.  

Here are some student work samples shown below.

  • These two samples, student one and student two, show answers given.  Both students show complete work, but I do not provide it here.
  • This is a sample of the first three problems.  Most of the students were able to get the first three problems correct.

Some of the student work is difficult to see, student one has all of the calculations correct except he or she states that there are no outliers.  Student two only has one correct answer and that is the range of the data set.  When looking at the final sample, this student also indicates that there is no outlier.  

Students seemed to be confused with how to test for the outlier using the IQR* 1.5.  Students will need further assistance with this test.


Calculator Activity

15 minutes

After providing students about 25 minutes at the beginning of the period to complete their description and supporting math problems for the military data, I review their work with the TI-Nspire Cx calculator.  I have students follow along with me using their calculators as well to check their work.  I walk around to quickly assess that all of the students have the statistics on their calculator for this univariate data set.

The students should get the following answers to show the spread of the data.

1.  Range= Max-Min= 214,120 - 110590=$103,530

2.  Interquartile Range= Q3-Q1=158560-111870=$46690

3.  IQR * 1.5= 70,035

Outlier > 113,180 + 70035= $183,215

Outlier< 113,180 - 70035=$43, 145

So there are two outliers, they are the two highest salaries of $186,044 and $214,120. 

4.  Variance= $1,439,476,987

5.  Standard Deviation of the Sample= $37,940.44

I model finding Standard Deviation for a Sample on the TI-Nspire Cx in the video below.

Self Reflection

10 minutes

After students have checked over their work, I want them to Self Reflect using a sheet that I provide each of them.  I want them to write comments in the box provided on the sheet of any misunderstandings or questions they may still have to clear up.  

I also want each of them to focus on the mistakes that they made.  Was their mistakes in applying the formula correctly, an arithmetic error, etc. .  I ask that students be specific in their self-feedback.  Even though they worked with a table partner for the Partner Activity, I want each individual student to provide comments and feedback about their own work that they provided.

For students that did not complete the work for the Partner Activity, I want them to provide a reason of why they did not complete it.  I also want them to provide comments and feedback on the parts of the assignment that they did complete.