Introduction to MINITAB

October 1991

Introduction to MINITAB

This is an introductory guide to MINITAB, an easy-to-use interactive general purpose statistics package on the VAX/VMS system. It is a set of procedures which stores, transforms and analyzes data. The most commonly used inferential and exploratory analytic procedures are included in this package, although it is somewhat limited in advanced statistics. Currently, the University of Washington is running MINITAB Release 7.2. MINITAB has an extensive online Help facility which may be accessed by typing help at the MINITAB prompt. For more extensive information on MINITAB, see the MINITAB Reference Manual (1989), MINITAB Handbook (1985) or the MINITAB Primer. Additional help is available by contacting Minitab's Technical Services Department at (814) 238-3280.

MINITAB Structure

MINITAB performs statistical procedures on data stored as worksheets (.mtw). The worksheet format resembles a data matrix, containing a different case in each row and a different variable in each column. Columns may be added to the worksheet directly using the read or set command or they may result from manipulating already existing variables to create new variables via data transformation and data analysis. For example, to add a column directly at the MINITAB prompt (MTB>), type Read C1 C2. To add a column through data manipulation at the MTB> Let C3=C1 +C2. This operation defines C3 as the total of C1 + C2.

The data is stored in the following manner:

Variables

When you request information on your data to be shown on the screen, it will also appear in this format. Worksheets are storage files written in MINITAB's own machine language which are only meaningful when edited within MINITAB. The worksheets can, however, be saved as permanent files to be used in future MINITAB sessions. In addition, some or all of the data contained in the worksheet may be written into an "output file" which is written in normal characters. This "output file", sometimes known as a "raw data file", can then be read by other programs or printed.

IMPORTANT In order to have printed output of your work session, you must tell MINITAB this at the beginning of your session. (For information on this see the "Saving MINITAB Work" section of this document).

MINITAB Worksheets on the VAX may contain up to 1000 columns (variables) and stored constants, and up to 100 saved matrices.

MINITAB Syntax

All commands in MINITAB begin on a single line with a four letter command name. Whenever the command name is longer than four letters, only the first four letters of the word need to be used. For example "retrieve" may be abbreviated as "retr". For clarity, commands in this document will be written in full with those letters which must be utilized for MINITAB to recognize capitalized. Most of the command names may then be modified by including additional parameters and specifications which tailor the command to your data set and procedures. For each command procedure, you must define which columns (variables) you wish to use. With some commands, you need to insert optional specifications in addition to the command name. If a single command line requires more than one line to enter, all lines but the last should end with an ampersand, or & symbol. When you utilize an &, the next prompt you receive will be CONT>. A command line may look like the following:

This command tells MINITAB you are now going to enter data into these three columns.

Notation:

Some MINITAB commands have subcommands that can be utilized. Each subcommand must have its own line. A command consisting of one command line and several subcommand line should have a semicolon (; symbol) after each command line with the last line ending in a period. For example:

(If you forget to add the period after the final subcommand, simply type it on the next line and hit <return>.)

The elements on a command line are separated by spaces or commas. Any text on the line that MINITAB does not recognize will be ignored. This feature allows you to insert explanatory notes to yourself. For instance, the next two commands are synonymous:

This feature may be especially helpful to users unfamiliar with the system.

MINITAB variables are usually referred to by their column numbers (C1, C2) but the terms "column" or "variable" may be used interchangeably in actual usage or conceptualization. The variables may be named and the names can be used in the command sequence in place of column numbers.

If you use variable names, always enclose them in single quotes, as in:

MINITAB Constants are generally referred to as K1, K2, K3 (up to a maximum or 1000). The total number of stored constants is equal to the number of columns. Constants are not stored in the worksheets as Ks, so if you wish to retain constants in the worksheet for future sessions, they need to be stored in columns. These columns are then known as "artificially long" columns; the value appearing in the constant column is the same for every case. A possible use of a constant might be:

In this instance, MINITAB will add 100 to each value in C1 and put the total in C3.

Entering and Leaving MINITAB

Below are commands that allow you to begin and end MINITAB sessions.

Saving Your Work in MINITAB

If you want to save your MINITAB worksheets (filename.mtx), when you being do the following:

To print out your work, you must enter the OUTFILE command. MINITAB will then record your results to an outfile. The OUTFILE command will divert the session or the output to a VAX file with a .lis extension. You may use this command at the beginning of a session or whenever you wish to save your results. After you exit MINITAB, you can then print your file to one of the campus printers.

To keep a record of your MINITAB commands in a printable file, type JOURnal 'file name' at the MTB>. (The name you give your command file should be enclosed in single quotes.) When you are finished, type NOJOurnal. This file will appear in your directory under the name you designated with an .tj extension. This file can then be used to check command accuracy or replicate previous work.

Accessing Help and Information in MINITAB

MINITAB has an extensive on line help system. To access help:

You are automatically returned to the MINITAB prompt when no more information is available on the topic you requested. A useful feature of the MINITAB system is the listing of statistical test available for analysis. This listing includes examples and a brief description of each test.

Entering Data Directly into MINITAB

To enter data directly into MINITAB, use the READ or SET command. READ expects data one row at a time; SET expects dat one column at a time.

 The entire sequence would look like this:

If you issued the INFO command to see your worksheet it would look like this:

If you had used SET instead of the READ command like this:

Your worksheet would look like this:

MINITAB is used primarily to manipulate numbers; however, it is possible to utilize character data as well. Each character data item (row of a specific column) may be up to 80 characters. Any numeral that appear in a defined character column will be treated as alpha characters and cannot be used for computations. To enter alphabetic data:

Naming Variables

The following command is sued to named columns or variables:

Once you name a column, you may use that name to refer to the column but the name must always be enclosed in single quotes, i.e. NAME C1 'age' DESC 'age'.

Correcting Data in the Worksheet

There are three commands that are useful for correcting data in a worksheet: LET, DELETE, and INSERT.

For example:

This worksheet has 2 columns C1 & C2

Mistakes:

(1) The underlined number, 39, should be 30.

(2) Case #2 was left out.

(3) Case #1 was inadvertently repeated as case #4 and case #5.

[Note: To add rows of data to the end of the columns, use:MTB> INSERT into C1..C2]

Case Selection (Using or Omitting Rows)

To select cases that have certain values (i.e. sex) for a particular analysis, use the following the COPY command with its subcommands USE and OMIT to specify the cases you wish to utilize.

Recoding Variable Values

To change a values of a variable (column) to another values, use the following:

This command may also be used to change codes that indicate missing values in data sets to '*' which is the MINITAB missing value.

Brief Summary of Commands

General Information:

Input & Output:

Manipulating Data:

One-Number Stats for Columns and Rows:

Use MINTAB and enjoy!