Introduction to Data Desk

This is not a step-by-step guide, but an outline of steps. Those of you familiar with Mac's have a head start. The rest will learn by doing...

Exercise 1. The following data are the marks (out of 100 and ordered by size) of 20 students in a mathematics exam:

30,35,37,40,40,49,51,54,54,55,57,58,60,60,62,62,65,67,74,89

Summarize these data in a way you think appropriate.

This requires that you enter data by hand. This is rare, but a good skill to learn, and a good introduction to other skills.

• Start Data Desk (double click on the icon.)

• Hold the button when the cursor is over the word "Data" at the top of the screen. A menu will appear. Move the cursor so it is over the word "New". A sub-menu pops up. Select "Blank Variable" by holding the cursor over these words and releasing the mouse.

In short-hand notation, we would say "Select Data:New:Blank Variable".

• A new window opens that says "Var0" (or "Var1"). Type the name of your new variable over this default name. For example, let's call this "Test Scores".

• A rectangular window opens. Place the cursor inside this window and click once. You can now enter the data. Hit return after each number. When you are finished, you can click on the "button" on the left hand side of this data window to close it.

Data Desk puts the result in the "Data" folder, which you can see on the right side of the screen. Double click to open this folder. You'll see that it contains a file called "Data". Double click on this, and you'll see this file contains our variable called "test scores."

• Click once on "test scores", and a large yellow "Y" will appear on top. This means that we have designated this the "y" (response) variable. You can now look at the menus at the top of the screen (For example, the "Plot" menu), and do those things to this variable.

Exercise 2. Open up Internet Explorer or Netscape and go to

http://www.stat.ucla.edu/~rgould/x401w00/anesthetics.dat

These data represent the number of minutes it took patients to open their eyes when anesthetized with one of four anesthetics. Are there differences?

To download these data:

• First you must save this file onto your computer. From the browser, under the "File" menu, choose "Save As". This puts the file (somewhere) on your harddrive. You can control where.

• Now, from within DataDesk, select "File: Import". A dialog box opens up to ask you to enter the name of the file that contains the data. You'll need to find your file called anesthetics.dat. Once you find it, select it.

• A new dialog box shows you the first line of the data file, and gives you a number of choices. Choose "Prompt for Variable Names." This will then prompt you, one at a time, to name each of the variables. Name the first "Treatment" and the second "Time".

• Click once on one of the variables. You will see it turn into a "Y" variable. If you hold down the shift key when you click, you'll turn it into an "X" variable. Play around with this a little bit. Can you create and "X" before you create a "Y"? Can they both be "X"? Can they both be "Y"?

• Make plots and summaries of these variables. Play around with the menu selections above.