INTRODUCTION: We will be using Macintosh computers, with a special statistics application program called MINITAB, for our data entry, graphics, and analyses. This session gets you started with the Mac and with MINITAB.
Note: The images in this tutorial are from MINITAB version 8.x; if you are using a version of MINITAB that is not 8.x (i.e., MINITAB 10.x), the images you see on your screen may appear different, and some items may be located in slightly different places under the menus. If you cannot figure out how to do something, please ask a lab assistant or your instructor for assistance.
STATISTICAL CONCEPTS: histogram, stem-and-leaf plots, boxplot, scatter plot, mean, median, mode, standard deviation, correlation, regression, prediction.
MATERIALS NEEDED: one Double Sided/Double Density 3.5" diskette.
LOCATIONS: MINITAB is available on the Macintoshes in LeConte 303A, on the Macintoshes in LeConte 127A, and on the Macintoshes in Physical Sciences 102. The hours for each lab are posted by the entrance to the lab.
I. HOW TO DRIVE A MACINTOSH
Follow the tutorial instructions below very carefully. First, move the mouse (the small box with a button on the pad next to the Mac) a little to see if the Mac is already on--if the screen stays blank, it's off. To turn it on, if you are using a small-screen Mac like the one depicted here, there is a switch at left on the back. Big-screen Macintoshes usually have an "on" button at upper right on the keyboard (with no label).
After the Mac is on, across the top of the screen you should see the Main Menu, which consists of the "words" , File, Edit, View and Special. This main screen itself is sometimes called the desktop. At bottom right is a picture of a trash can. These little pictures are called icons. At top right may be a rectangle or something like it with a name below it- this is the icon and name for the computer's hard disk drive, which is where the computer's long-term memory lies. These notes assume the Macs you're using have hard drives. If not, your instructor will provide modifications as needed.
Your main control for driving a Macintosh is the mouse. Just as you had to practice with the controls of a car before taking it out on the freeway, you will need to develop some basic mouse skills to get around on the Mac. The skills are: pointing, clicking, dragging, and selecting menu items.
POINTING: Hold the mouse lightly between your thumb and middle finger. Move it around a bit on the pad and see how it controls the arrow on the screen. If you accidentally get to the edge of the pad but want to move the arrow more in that direction, just pick up the mouse and place it anywhere else on the pad and keep rolling from there. Now (without pushing the mouse button) practice pointing by moving the arrow until it just touches each of the screen objects. Point to each corner of the screen in turn, in clockwise order and then in counter-clockwise order.
CLICKING: This is where you put the arrow on an icon or a menu item and push-and-release the mouse button. Try clicking on the . Did you see a list appear and then disappear? That was the apple menu. If you want to look at it longer, point at the again and this time click-and-hold the button. When you let the button go, the menu disappears.
Let the button go now, and point-and click on the trash can. It should change to a dark color, which means it has been selected. Now click twice on the trash can as quickly as you can. This is called double-clicking. The empty box that opens on the screen is called a window (specifically, it is the trash window). We'll play with it more later, but for now close the trash window by pointing and single-clicking on the little box in its upper-left corner (which is called the close box).
So, in summary, there are at least three variations on clicking:
DRAGGING: Click-and-hold on the trash (don't double click--that will open the trash window), and while still holding the button, move the mouse on the mouse pad. An outline of the trash can should move as if it is pasted to your arrow. Drag it over to the lower left corner. Now drag it back. Drag it clockwise to all four corners of the screen. Now drag it counter-clockwise. O.K., drag it back to the lower right corner where it belongs.
SELECTING MENU ITEMS: Click-and hold on the . You'll see the apple menu, which is a list of mini-programs called desk accessories you can use for simple things like checking the time or doing a calculation. Let's check the time: with the mouse button held down, move the arrow slowly downscreen from the . Notice each menu item goes to white-on-black when it is touched by the arrow. Make the Alarm Clock item change to white-on-black and then, without moving the mouse, let go of the button. You have just selected that menu item; as a result, you should now have a small box somewhere on the screen showing you the time, somewhat like the illustration below. Close this desk accessory now by clicking in its close box at left of the time shown.
Congratulations! If you accomplished all the above, you're certified a safe beginning Macintosh driver. A couple more beginning topics are needed before we introduce the data analysis program, MINITAB.
MORE ABOUT WINDOWS: Nearly all Macintosh work is done in windows of one sort or another. There are several things these windows have in common. As an example, open the trash window again by double-clicking on its icon. Across the top of every window is the title bar. You can drag the window anywhere you want on the desktop (screen) by clicking-and-holding on the title bar and using it to drag. Try it by dragging the open trash window to the top of the screen.
There are two ways to resize the window: (a) click once in the box at top right and the window gets very big. Click again and it returns to its original size; or, (b) click-and-hold in the box at lower right of the window (the resize box), and then drag. The window changes shape and size depending on where you drag that corner.
This finishes our introduction to the Macintosh. Everything discussed above carries over to any Macintosh computer anywhere. We will learn more Macintosh basics as they become helpful, but now we're ready to become acquainted with MINITAB.
You may have noticed, in particular, that we did not tell you how to shut down your Mac. That's because it should be left on most of the time; too much turning on and off can wear out the hard disk drive. The lab manager will shut the Macs down at the end of the day.
II. AN INTRODUCTION TO MINITAB
MINITAB is a very powerful, yet user-friendly, data analysis application program. In this demonstration, we will use all of the commands that will relate to the topics that are covered in Chapters 4 and 5 in our textbook. Throughout this demonstration, if you have any problems or questions, feel free to ask a lab assistant or your teacher for assistance.
You can launch MINITAB by following these steps:
a) Double-clicking on your hard-drive's icon (upper right of the desktop).
b) In the new window, double click on the folder icon entitled MINITAB.
c) In the next new window, double click on the fancy icon entitled MINITAB.
You should see the MINITAB logo, and after another moment you'll see a window, the data window, named "untitled worksheet" and a new set of menus across the top of the screen. You might also notice the edges of another, inactive, window behind the data window.
SCROLLING IN WINDOWS: Sometimes a Macintosh window gets too large to display on screen in its entirety. For example, all the data you enter may not show in the data window at once. As you're typing, the window should automatically give you more room, but early entries will then disappear from view. If you want to look at what's at the top of the data window, you can scroll up the window by clicking-and-holding on the upscroll arrow (see the following illustration) that appears near the upper right corner of the window (try it). Or, you may have to scroll down the window by clicking-and-holding on the downscroll arrow at bottom right (try it). Or, the fastest way, for really large windows: the scroll box between the scrolling arrows shows where the currently visible part of the window is located in the complete window; if the scroll box is at the top, you are looking at the top of the entire window's contents, if it is a third of the way down, you are looking at contents 1/3 of the way through the window, and so on. You can drag the scroll box to look at any part of the complete window. For example, drag the scroll box to the top of its bar and release. Now you see the top of the window's contents. Now, drag it to the bottom of its bar and you will see the bottom of the window's contents. As soon as any Macintosh window gets too big to display in its entirety, scrolling arrows will appear. This is true for all Macintosh windows, not just in MINITAB.
When we enter data into the worksheet, we can do so one row at a time, using the tab key. Data can also be entered one column at a time. To do it this way, you would click in the first cell of the column, type the entry, then push the return key and you will automatically move to the next cell down.
After inputting data, always look back at it and double-check each number to make sure it is input correctly. Always double check data upon inputting it, as input errors are very common, and if they are not corrected, all calculations will be in error, too. If it is not too disruptive, the best way to do this is to have someone else quietly read the data back to you while you check. If you find a mistake, click in that box and retype the value.
We've left out an important step in the creation of any data set, and that is to save the data to a minidisk. Under the File menu, select Save Worksheet; give your data set a name and save it on your minidisk. It may be necessary for you to click on the Drive button to select your minidisk as the recipient of the file.
Sometimes after inputting data, you will notice that some of the MINITAB menu items are in gray lettering, and that these items cannot be accessed. To correct this, click in any empty cell of the worksheet. The menu items' lettering should turn black again, and these items will become accessible.
When we do work on data, we can refer to variables by their column numbers C1, C2 etc. or by more meaningful names we give them. Name the variables for this data set:
Now begin to input the data:
Continue typing the times and lengths for all of the following data set in this fashion. If you make a mistake, use the delete key, or click in the box containing the mistake and retype the entry. If you get to the bottom of the data window, it should give you more room automatically.
Note that this data is a collection of the number of miles that a typical Clemson University student could plow with his fixed-up hot-rod tractor during the recorded number of minutes.
MODIFYING DATA: AN EXAMPLE. MINITAB makes routine calculations a snap. Let's use it to compute the mean, median, mode, and standard deviation of both of our columns of data.
To compute these descriptive statistics,
After some delay, that window should close. The window which has been behind your data window all along, called the Session window, has now come to the front (become active). After a few seconds the descriptive statistics of the data appear there (see the section entitled `THE FIVE MINITAB WINDOWS' for more details on the Session window).
GRAPHICAL DESCRIPTION OF A VARIABLE: It is difficult to see patterns in large collections of numbers just by looking at them in tables. To better understand the data, we could make a descriptive plot of some sort. MINITAB offers three possibilities to graphically describe a single variable's distribution:
We can make a histogram, a "picture" of the distribution of the data, like so:
A new window should now appear containing your histogram for the variable 'Time'. In order to create a stem-and-leaf plot or a boxplot, follow the above instructions while substituting either Stem-and-Leaf or Boxplot for Histogram. Note that the stem-and-leaf plot will appear in the Session window, while the boxplot will appear in a separate window as did the histogram.
We're done modifying and inspecting the data, and in a minute we'll get a printout to take home. First, let's look at some of the other windows.
THE FIVE MINITAB WINDOWS: Go to the Windows menu and click-and-hold. You will notice several items, corresponding to different types of windows that MINITAB can display:
We will finish the session by obtaining a printout of the Session window, a record of the work you've done, which will also contain a printout of the final data set. The instructions below assume you will be printing on an Imagewriter printer. If not, your instructor will explain any necessary modifications to the instructions, which will be very minor.
The printer for your group of Macintoshes should soon begin printing your session window. When it is finished, carefully remove your output from the printer as follows:
Now, make a printout of the graph windows by repeating the steps above after selecting the window desired for printing.
Below is a sample of what your printout for the Session window might look like.
Worksheet size: 38000 cells
MTB > GHistogram 'Time'.
MTB > Describe 'Time' 'Length'.
N MEAN MEDIAN TRMEAN STDEV SEMEAN Time 14 29.07 26.50 27.83 12.87 3.44 Length 14 7.464 7.350 7.450 0.580 0.155
MIN MAX Q1 Q3 Time 11.00 62.00 19.75 35.50 Length 6.600 8.500 7.075 7.850
MTB > GBoxPlot 'Time'.
MTB > Stem-and-Leaf 'Time'.
Stem-and-leaf of Time N = 14
Leaf Unit = 1.0
1 1 1 3 1 79 5 2 03 (4) 2 5678 5 3 24 3 3 3 4 03 1 4 1 5 1 5 1 6 2
BE SURE TO WRITE YOUR FULL NAME ON ALL PRINTOUTS TO BE TURNED-IN TO YOUR INSTRUCTOR!
BE SURE TO CIRCLE OR LABEL ALL RELEVANT PARTS OF THE PRINTOUT!
(THE EXERCISES CHECK NOT ONLY THAT YOU CAN PRODUCE THE RESULTS, BUT ALSO THAT YOU CAN RETRIEVE ALL PERTINENT RESULTS FROM THE PRINTOUT.)
QUITTING MINITAB: Under the File menu, select the item Quit. MINITAB may open a window asking you if you want to save the data. Ordinarily you would, so click Yes; if MINITAB just quits, no unsaved changes were made to the data set.
MINITAB Assignment #1
Please direct all questions regarding STAT-110 to your instructor or to the director of STAT-110, Dr. Todd Ogden at firstname.lastname@example.org.
Mail comments regarding this presentation to W. Scott Street, IV at email@example.com.
© 1996 by W. Scott Street, IV