MINITAB ON THE MACINTOSH I


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

Mac Image

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" Apple Logo, 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.

Mac Menu Bar Image

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 Apple Logo. 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 Apple Logo 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).

Trash Window Image

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 Apple Logo. 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 Apple Logo. 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.

Alarm Clock DA Image

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.

MINITAB Window Image

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.

Untitled Worksheet Image

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.

ENTERING DATA:

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:

  1. Click in the first empty box immediately under C1, and type: Time.

    Warning: do not type these variable names in the row labeled 1.
    You'll have to retype the entire data set over again if you do.

  2. Hit the Tab button; this should move you one box to the right. Or, click in that box.

  3. Type: Length.

Now begin to input the data:

  1. Click in the first open box in column C1, under the word Time. Type: 17.

  2. Tab to the next cell, and type: 7.1.

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.

Worksheet with Data Image

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,

  1. Click-and-hold on the Stat menu.

  2. Keeping the mouse button depressed, move down the menu until the item Basic Statistics is highlighted; don't let the mouse button up. Notice that another menu, a submenu, appears.

  3. Without letting the mouse button up, carefully move the pointer straight to the right until it touches the submenu; if you slip, you'll have to go back to (b) and try again.

  4. Move down this submenu until the item Descriptive Statistics is highlighted; then let the mouse button go, thereby selecting this item.

  5. In the newly opened window, at upper left is a box with a list of the data set's numeric-variable columns (C1, C2) with their names. Click on C1, then click in the box titled Select. Now repeat this for C2. You have just selected these columns for the calculations. (see the following illustration)

  6. Click the OK button.

Descriptive Statistics Image

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:

  1. the histogram

  2. the stem-and-leaf plot (also called a stemplot)

  3. the boxplot (also called a schematic plot).

We can make a histogram, a "picture" of the distribution of the data, like so:

  1. Under the Graph menu, select the Histogram item.

  2. In the upper left of the newly-opened window, double-click on Time. That word should now appear in the Variables window.

  3. Click OK.

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:

  1. The Data window shows the worksheet in row-column form. From here, you can create new variables, modify old ones, sort data, subset the data, and much more.

  2. The Info window gives summary information about a data set. Select that item now. You should see a list of columns C1-C2, with names. The Info window is not extremely useful to us, since we will use mostly small data sets which we can inspect adequately in the data window.

  3. The Graph window will display certain graphs and plots that we will make (for example, histograms and box plots).

  4. The Session window will be valuable to us. Select that item now under the Window menu. It should look somewhat like the next illustration. Besides the stem-and-leaf plot, there are other lines beginning with "MTB>" or "SUBC>". The fact is, though every action we've carried out has been done by selecting menu items, each could also have been done by typing and entering commands in the Session window. Some types of work are much easier to do this way. For example, click just to the right of the last MTB> line (the MINITAB prompt), and type: Note this printout belongs to ______ (fill in your name). Now, push return. That was a MINITAB comment--any command beginning with Note is ignored my MINITAB and is just a user's comment. Next to the new MINITAB prompt, type: Print C1-C2. Now, push return. The computer responds to this command by printing the specified columns in the session window. Once one gains enough familiarity, typing commands in the Session window can be faster than selecting menu items. You can even write entire MINITAB programs, called macros. Also, MINITAB versions exist for IBM P.C.'s, microcomputers, work stations, and mainframes, and these usually use commands instead of menus. The command version of MINITAB existed long before the menu-driven version.

    Session Window Image

  5. The History window is like the Session window only less messy, and you can't enter any commands in the History window.

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.

Printer Dialog Image

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:

  1. On the printer control panel, push the Select button.

  2. Push the form feed button.

  3. Push the Select button again.

  4. Gently tear off you hard copy, without yanking on it.

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.


Homework

MINITAB Assignment #1

(Solutions)


T.O.C.BackNext


Please direct all questions regarding STAT-110 to your instructor or to the director of STAT-110, Dr. Todd Ogden at ogden@stat.sc.edu.

Mail comments regarding this presentation to W. Scott Street, IV at street@stat.sc.edu.


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© 1996 by W. Scott Street, IV