Math 321, Lab 2: Correlation Coefficients and Scatter Plots
Please do the following exercises with the MINITAB software package. There is one exercise, at the end, which asks you to print something off and hand in. You may work in groups, but use separate computers. The papers you hand in should contain your name only. You may also use some of the techniques of this lab exercise to do your homework. See other handouts for information on how to start MINITAB and how to shut it down. This Lab exercise will refer to Data Set 8, which appears below.
   x:    70    72    72    77    79    81    84    90    92    99
   y:    400    550    700    600    800    900    1100    1200    1500    1900
  1. In this first exercise, we will compute x1 + x2 + . . . + xn. Start MINITAB. Enter the x-values from Data Set 8 into rows 1 through 10 of column C1 of your MINITAB worksheet. Then, starting at the top of the screen, click on Calc->Column Statistics->Sum. Type C1 as your input variable. Then click on "OK." The answer will appear in the Session window. You may have to scroll to see it. The answer should be 816.
  2. In this exercise, we compute the sum of the squares of x1, x2, . . . , and xn. Starting at the top of the screen, click on Calc->Column Statistics->Sum of Squares. For the input variable name, type C1. Then click on "OK." The result, 67,420, should appear in the session window.
  3. In this exercise, we will compute x1y1 + x2y2 + . . . + xnyn. Enter the y-values from Data Set 8 into rows 1 through 10 of column C2 of your MINITAB worksheet. Thus column C1 will contain the x-values, and column C2 will contain the y-values. Next, start at the top of the screen, and click on Calc->Calculator. In the field for "Store result in variable:" enter C3. Be sure to type C3, not C1 or C2. In the box for "Expression:" enter "C1*C2", without the quotation marks. Then click on "OK." Minitab should now have inserted values into the first twenty rows of Column C3. Now sum these values. Do so by starting at the top of the screen and clicking on Calc->Column Statistics->Sum. Type C3 as your input variable, and click on "OK." The result, 826,800, should show up in the Session window. You may have to scroll in order to see it.
  4. In this exercise, we will calculate Pearson's sample correlation coefficient. Start at the top of the screen, and type Stat->Basic Statistics->Correlation. In the box for variables, type "C1 C2" (without the quotation marks, but with the space between C1 and C2). Then click on "OK." The result, .973, should show up in the Session window.
  5. In this last exercise, we will construct a scatter plot. Start at the top of the screen and click on Graph->Scatterplot->Simple->OK. In the field for x-variables, type C1. In the field for y-variables, type C2. Then click on "OK." If your scatter plot looks good, print it. To do so, proceed as follows. First, click on any part of the scatter plot. Then, starting at the top of the screen, click on File->Print Graph->OK. Supply a print job name, and click on "Print." Go over to the lab monitor and ask for your output. Write your name on it, and hand it in by the announced due date.

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Contact Person: Larry Peterson
E-mail: lawrence.peterson@und.nodak.edu
Phone: (701) 777-4609
Date of most recent update: 23 February 2009
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