Minitab in M 358K

Using Minitab in M 358K

General Comments

Remember that when using a computer, things sometimes go wrong. If what you first try doesn't work, try again or try a reasonable variation. Follow any instructions in dialogue boxes that may appear. If on-line help is available, try it. If a lab proctor or classmate is available, try asking them.
To avoid excess frustration from losing work, save your work often. You can save graphs or the contents of the Minitab Session window or Worksheet by using the appropriate Save command on the File menu.

Using Minitab on a Math Department Computer

You can get an account in the "Big Lab," RLM 7.122.
There is no on-line help available for Minitab in the math department lab.
To open Minitab in the math lab, first log on. Then click the icon in the lower left of the screen to get the application menu. Go to Minitab. It will take a while for Minitab to open.
The data files from the textbook have been loaded into the math department computer system. To access one of these files, select Open Worksheet from the File menu. A dialogue box will appear. In the "Files of type" box, scroll to "All." In the "Look in" box, scroll to Root(z). Then successively double-click on d, dell7v1, class71, courses, M358K, PCDataSets, Minitab. Then double click on the chapter number, then on the exercise or table. (Exercise files start with "ex," table files start with "ta.") The data should then appear in the Worksheet.
You should be able to save a worksheet to your home directory.
You can also open Star Office in the same way you opened Minitab. You can cut and paste from the Session Window of Minitab to Star Office, but you can't copy and paste graphics.
To log out, use the same menu from the icon.

Using Minitab on Another Computer

You will need to get textbook data files either from the CD included with your textbook, or from the book's website.
The instructions below are for Minitab 14 for Windows. If you are using another version, instructions will sometimes vary from what is given below, but you can probably figure out what to do from what is given here and on-line help.

To Make a Stemplot, Histogram, or Box-Plot

Open the data file, or enter data by hand in the Worksheet.
From the Graph menu, select Stem-and-Leaf, Histogram, or Box-Plot. (In some older versions of Minitab, you need to select Character Graphs before obtaining a menu listing Stem-and -Leaf.)You should get a dialogue box. Now do any one of the following:

Type c and the column number of the variable you want (e.g., c1, c2, etc.) in the Variables box.

        Type the name of the variable (as listed at the top of the column) in the Variables box.
        Type the name of the variable in single quotes.
        Click on the entry in the box in the left of the dialogue box, then click Select.
        Double click on the entry in the box at the left of the dialogue box.

Click OK to get the graph or plot. (If you've made a stem-and-leaf plot, think about whether it differs from the one you would do by hand. What is the stuff at the left?) (If you've made a box-plot, notice that it is different from what is described in the textbook.)
To split the stems on a stemplot: Repeat the preceding step, but put 5 in the box that says “increment” in the dialogue box. What does this do? Experiment with other increments.
To change the number of bins in a histogram, click "options" before you click "OK". You can put in the desired number of bins. You can specificy whether you want to organize the bins by mid-point or by cut-point. You can use shorthand notation such as 10:50/5 to mean that cut-points or mid-points start at 10, end at 50, and increase in increments of 5.)

Notation Used in the Remainder of These Notes:

XX > YY > ZZ means:

From the menu XX, choose YY; then choose ZZ from the resulting menu.

To find mean, standard deviation, median, and quartiles:

Use Stat > Basic Statistics > Display Descriptive Statistics. (The last menu might be called just Descriptive Statistics on older releases.) You can get statistics on more than one variable at once by putting all the variables of interest in the dialogue box.

To make a normal quantile plot:

First calculate the expected values. Use Calc > Calculator. Enter the column where you want to put hte expected values in the “Store result ...” box. Scroll down to Normal scores in the Function menu. (In some versions, you may need to click on "expressions" to get the Functions box.) Click on Normal scores, then the Select button (or just double-click). Insert the column where your data is stored. Click OK.
Now make the normal quantile plot as a scatter plot (see below). Use your original data for Y and the expected values (“normal scores”) you calculated in step (a) as X.

Note: Graph > Normal Probability Plot will give you a normal probability plot, which is like a normal quantile plot with the axes reversed.

To make a scatter plot:

Use Graph > Plot to get the scatter plot dialogue box. In the box, enter the column of the Y variable and the X variable, using any of the methods listed above. (Note that Y is first.) Then click “OK.”
To make a scatter plot with different symbols for different groups, proceed as above, but also do the following:

a. Use the pull-down menu in “For each” to choose “group”.

b. Enter the column with the group labels (e.g., for male or female) in the space under Group Variables. (You can use Edit Attributes to choose symbols other than the default.)

Experiment with the other buttons to see how to do things like changing the labeling on the axes, starting the picture at a different place, etc.

To calculate the correlation coefficient r

Use Stat > Basic Statistics > Correlation. Enter the two variables (columns) you want the correlation of, and click OK. Ignore any extra information you get.

To calculate a function of every entry in a column (e.g., to find 1/x for every x in a column)

Use Calc > Calculator (or Mathematical Expressions on some older releases). “Variable” is where you want the calculations to be stored. Type the expression you want in terms of the column or variable you want to transform. (e.g., 1/c1 will give the reciprocals of the entries in c1.) You can use the keypad provided in the dialogue box rather than the regular keyboard, if that is more convenient. Use * for multiplication and ** for an exponent (e.g., (c1)**2 for c1-squared). For functions like logarithms, as well as things like min and max, you can use the scroll down menu at the right of the dialogue box. Remember parentheses.

To find a regression equation

Use Stat > Regression > Regression. You will get lots of extra stuff you should ignore when we're first doing regression.
To plot the regression line and data together, use Stat > Regression > Fitted Line Plot. This may take longer to appear than other things you have done so far.
To find predicted values and residuals for your original data points, proceed as to find the regression line (above), but click the “storage” box, then check the boxes for “residuals” and for “fits” in the new dialogue box before clicking OK. The predicted values will be stored in a column labeled FITS N and the residuals will be stored in a column labeled RESI N, where N is the number of times you have stored residuals on that worksheet. Also note that points with large residuals may be mentioned on the output in the Session window.

To make a scatter plot with two regression lines plotted on it

First calculate the regression lines and save the predicted values (fits).
Then use the Plot dialogue box to set up the scatter plot, but before you click OK, choose Line from the pull-down Annotation menu. In the first row of the first column of the resulting dialogue box, type in the names (separated by a space) of the columns containing the x-values and the fits for the first regression line. Fill out the remaining two columns of the first row as you wish. Do the same for the second regression line in the second row. Now click the OK’s.

Copying Columns and Finding Row or Column Sums

You can use Copy Columns from the Manip menu to copy one column to another, then Delete from the Edit menu to delete entries.
You can find the sum of a row or a column by using Row Statistics or Column Statistics from the Calculate menu.

To find the p-value for a particular t-value

Use Calc > Probability Distributions > t...

Check “Cumulative probability.” Enter the degrees of freedom in the appropriate box, then check “Input constant” and enter the t-value in the box. Click OK, and the left-tail probability should appear in the session window. (You can figure out what to do if you need the right-tail probability.)

To do t and z procedures and tests for proportions:

Use Stat > Basic Statistics > (t, z, etc. as appropriate). Then check the appropriate items and fill in the appropriate boxes in the dialogue box. (The item “mean’ in the one-variable t-test refers to the value of the mean specified in the null hypothesis.)

To do a chi-squared test:

Put the observed counts from your two-way table in columns in the Minitab worksheet. Do not include any totals.
Use Stat > Tables > Chisquare test. Enter the columns contaning your counts in the appropriate place in the dialogue box. Click OK.
Results will appear in the session window.

To find confidence and prediction intervals for regression

Set up regression as above, but before you click OK, click Options.
In the box labeled, "Prediction interval for new observation," enter the x-value for which you want the confidence or prediction interval.
Enter the desired confidence level.
Click “confidence limits” and/or “prediction limits," depending on what you want.
Now click OK and run the regression.
The confidence and/or prediction limits will appear in the session window, and possibly on the worksheet, depending on your version of Minitab.