Material for the MTH 113 Computer Lab Sessions, Fall 2010

11/29/10

We are going to analyze two-dimensional data today. Given two random variables, we want to graphically analyze whether one depends on the other in an approximately linear way. I'm going to explain the general setup at the whiteboard.

Here is what I would like you to do today:

• Download the file linked to the following icon (by right-clicking it and choosing "Save link as...").
• Read it into columns c1 and c2. To do this, click "File" in the Minitab Menu, choose "Other files"- "Import Special Text..." and put c1 c2 in the text field named "Store data in column(s)". Click OK, then navigate to the place where you stored the file, and make sure you set the file type to "All Files (*.*)". Then double-click the file name, P612Ex2.txt.
• The data that appeared in columns c1 and c2 are taken from the textbook (page 612, example 2). Label column 1 "Advertising" and column 2 "Sales".
• To represent the data graphically, click "Graph" in the Minitab menu bar, and choose "Scatterplot...". Choose "Simple", then click OK. In the next window, put column C2 in the Y-column and column C1 in the X-column. This can be done by double-clicking C2 and then C1 on the left hand side of the window.
• Look at the scatterplot. Do you understand the meaning of the dots? Are they roughly located along an imaginary line?
• Now, let the computer calculate a line around which the dots are arranged most closely (in a sense to be made precise in class soon). To do this, repeat the steps above, but this time, instead of selecting "Simple", choose "With Regression". Don't close the window containing the graph!

Is the line located like the one you imagined? Let's look at two more examples.

• Download the file linked to the following icon: . Load its contents into columns c3 and c4. Label these columns "Age" and "Rent reduction" (the numbers are taken from the textbook, page 641, example 1).
• Make a scatterplot with regression of these data (putting c4 into the Y column and c3 into the X column). Keep the window containing the graph!
• Compare the two graphs containing the regression line.

• Now download this:
• Load the file contents into columns c5 and c6.
• Make a SIMPLE scatterplot (without regression), putting c6 into column y and c5 into column x.
• Looking at the scatterplot, do the dots seem to be arranged along a line?
• Now produce a scatterplot with regression of these data. Does the line seem meaningful to you?

You're almost done now.

• To finish, put the three scatterplots with regression lines into one layout, add your name to the layout, print it, and hand it to me.
• Shut down your computer.