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GUIDE TO MINITAB Prepared by Maria Rios BUSINESS STATISTCS 41000 C. ALAN BESTER FALL 2009 FALL 2009 BUSINESS STATISTICS 41000 1. INTRODUCTION Minitab is a Statistical Analysis software that allows to easily conduct analyses of data. This is one of the suggested software for the class. This guide is intended to guide you through the basics of Minitab and help you get started with it. 2. USING MINITAB 2.1. Using Minitab in Harper and Gleacher Center Minitab can be found in the computer lab computers. In order to load the software go to: START -> PROGRAMS -> MATH & STATS -> MINITAB 15 -> MINITAB 15 STATISTICAL SOFTWARE ENGLISH 2.2. Using Minitab in your Computer You can use Minitab 15 on your computer by taking advantage of the academic agreements Minitab 15 has. All the information can be found in http://www.mintab.com/en-US/academic/licensing-options.aspx 2.3. Minitab Resources The main source of help for Minitab can be found in the built-in help menu. For it go to HELP -> HELP. GUIDE TO MINITAB 15 2 FALL 2009 BUSINESS STATISTICS 41000 Additionally, there are several useful Minitab Resources. 1. Meet Minitab http://www.mintab.com/uploadedFiles/Shared_Resources/Documents/MeetMi nitab/MeetMinitabEN.pdf 2. Minitab Tutorial – University of Reading http://www.reading.ac.uk/nmsruntime/saveasdialog.aspx?lID=35672&sID=143 849. 3. STARTING MINITAB 3.1. Minitab Project and Worksheets Minitab has two main types of files, projects and worksheets. Worksheets are files that are made up of data; think of a spreadsheet containing variables of data. Projects are made up of the commands, graphs and worksheets. Every time you save a Minitab project you will be saving graphs, worksheets and commands. However each one of the elements can be saved individually for use in other documents or Minitab projects. Likewise you can print projects and its elements. 3.2. Understanding the interface After loading Minitab, you will either open an existing project or a new one. GUIDE TO MINITAB 15 3 FALL 2009 BUSINESS STATISTICS 41000 In either case, the following window structure appears Menu bar Toolbar Session Window Worksheet window There are 4 areas in the screen, the Menu bar, the Toolbar, the Session Window and the Worksheet window. 3.2.1. The Menu bar: You can open menus and choose commands. Here you can find the built-in routines1. 3.2.2. The Toolbar: Shortcuts to some Minitab commands. 3.2.3. Session Window: Displays output and lets you type commands. In order to be able to type commands in the Session window you need to enable2 this option. To do so go to EDITOR -> ENABLE COMMANDS. The Session Window will now look like 1 Minitab has a large number of built-in routines that allows you to do most of the basic data analysis. Commands can also be typed into the Session Window, to either replicate the built-in routines or to create a more tailored data analysis. 2 The “MTB>” prompt should be visible in the Session Window. GUIDE TO MINITAB 15 4 FALL 2009 BUSINESS STATISTICS 41000 It is recommended to always perform this step when you first you get into Minitab. 3.3. Worksheet Window: Data in Minitab is stored in a worksheet of columns and rows. Typically, each column contains the data for 1 variable, with 1 observation in each row. Columns are numbered C1, C2, C3, … , while rows are numbered 1, 2, 3, … 3.3.1. Changing column name. You can change column names by clicking the field below the column number, typing the name and then hitting return. You can also change the name using commands (see section 10.2.2) 3.3.2. Editing column data. Column data can be edited. You can also copy and paste data into the columns. You can paste .txt and Excel data with no problem. 4. LOADING DATA IN MINITAB Minitab files are organized as “projects”. Each project will contain all the data you use and the commands and analysis you perform on the data. You can open a new, empty worksheet at any time. In this empty worksheet you can copy, paste and type the data you need by simply working on the worksheet as you would on any spreadsheet. 4.1. Opening an existing Worksheet (Minitab type file) Within a project you can open one or more files that contain data. When you open a file, you copy the contents of the file into the current Minitab project. Any changes you make to the worksheet while in the project will not affect the original file. To open a Minitab type file 1. Choose FILE -> OPEN WORKSHEET GUIDE TO MINITAB 15 5 FALL 2009 BUSINESS STATISTICS 41000 2. Look for the file you want to open. Should be a .MTW or .MPJ type file. Select the file and click Open. 3. If you get a message box indicating that the content of the file will be added to the current project, check “Do not display this message again”, and then click OK. 4.2. Importing data (Non – Minitab type files) 4.2.1. Opening Excel files 1. Choose FILE -> OPEN WORKSHEET 2. In the field “File of Type” select EXCEL (*.xls, *.xlsx) from the drop down menu. 3. Choose the file you wish to open, and click Open. 4. If a message box appears see step 3 of opening an existing Minitab Worksheet (see section 4.1, 3) 4.2.2. Opening a text file 1. 1. Choose FILE -> OPEN WORKSHEET 2. In the field “File of Type” select TEXT (*.txt) from the drop down menu. 3. Click OPTIONS and the following dialog box will appear. GUIDE TO MINITAB 15 6 FALL 2009 BUSINESS STATISTICS 41000 4. Go to the “SINGLE CHARACTER SEPARATOR” option. The data on the text file is usually separated by spaces or tabs. Choose the appropriate option. If you are unsure how the data is separated, another option is to use the number of data rows. Just introduce the number of data rows in the “NUMBER OF DATA ROWS” box. 5. Click OK. 6. The results will appear in the worksheet window. Note: This can be sometimes a little tricky as you can get a file that does not the have the data in the format that you want. If this happens, close the worksheet where the data is placed and try importing it again, changing some of the options in step 4. This is a trial and error procedure; so don’t panic if you don’t get it in the first attempt. 4.2.3. Copying data to Minitab Copying data to Minitab works like copying data to any other type of spreadsheet (eg. Excel). 1. Copy the data you wish to use in Minitab. 2. Go to the position where you want to copy the data in the desired Minitab worksheet. If you wish to paste a cell with a Header or Name, make sure that you stand in the variable name cell (cell below the number of the column C1, C2, etc). 3. Go to EDIT -> PASTE CELLS to paste the data. 4. Sometimes when you copy data, Minitab reads it in a wrong format, eg. As a text when is numeric. To solve this problem, select the problematic column(s) and go to DATA -> CHANGE DATA TYPE -> CHOOSE THE DESIRED FORMAT. The most useful format is numeric. GUIDE TO MINITAB 15 7 FALL 2009 BUSINESS STATISTICS 41000 The following dialog box appears. Choose the variables you want to modify and where you want to store them. The storage variables can be the same variables as the ones you are modifying. Then hit OK. 5. Ways to Analyze Data Analysis in Minitab can be done in two ways: using the Built-In routines or using command language in the Session window. These two can be used interchangeably. 5.1. Built-In routines Most of the functions needed in basic and more advanced statistical analysis are found as Minitab Built-In routines. These routines are accessed through the menu bar. To use the menu commands, click on an item in the menu bar to open a menu, click on a menu item to execute a command or open a submenu or dialog box. 5.2. Command Language To be able to type commands in the Session window, you must obtain the “MTB>” prompt (See section 3.2.3). All commands are then entered after the GUIDE TO MINITAB 15 8 FALL 2009 BUSINESS STATISTICS 41000 “MTB>” prompt. All command lines are free format, in other words, all text may de entered in upper or lowercase letters anywhere in the line. NOTE: This guide focuses mainly on using the Built-In routines. All the explanations and examples that follow will be done using Minitab’s Built-In routines. A brief introduction to using Minitab commands is found in section 10. 6. Descriptive Statistics 1. To obtain descriptive statistics of a variable or set of variables, go to STATS -> DISPLAY DESCRIPTIVE STATISTICS 2. And a prompt window should appear. In the window select the variable(s) you want to analyze and click ok. 3. Results will be presented in the Session window as follows. GUIDE TO MINITAB 15 9 FALL 2009 BUSINESS STATISTICS 41000 7. Graphs Graph drawing built-in routines in Minitab can be found under the GRAPH menu in the menu bar. On the Graph Menu you have several types of plots that you can choose from, and that you can use to produce your desired plot. Below is an explanation of how to use the most popular graph routines. Minitab graphs will appear as separate windows that are considered part of the project, however they can be saved and copied for use in documents. Plots can be customized by modifying the plot options. 7.1. Simple Scatterplot 1. For a simple scatterplot, go to the SCATTERPLOT submenu. The following dialog box appears. 2. Choose the simple type of scatterplot, (the with regression type is also common). 3. The following dialog box appears. Choose the variable to go on the y-axis and the variable to go on the x-axis, and click OK. 4. Minitab will produce a plot as shown here. GUIDE TO MINITAB 15 10 FALL 2009 BUSINESS STATISTICS 41000 7.2. Simple dotplots 1. For a simple dotplot, go to the DOTPLOT submenu. The following dotplot dialog box appears. 2. Choose the Simple dotplot and the following dialog box appears. Choose the variable you want to plot and click OK. 3. Minitab produces a plot as shown here. GUIDE TO MINITAB 15 11 FALL 2009 BUSINESS STATISTICS 41000 7.3. Simple Histogram and Simple Histogram with fit 1. For a simple or simple with fit histogram, go to the HISTOGRAM submenu. The following histogram dialog box will appear. 2. Choose the type of histogram you want. 3. The following dialog box appears. Choose the variable you wish to plot and click OK. 4. Minitab will produce plots as presented below, according to the type of histogram chosen. GUIDE TO MINITAB 15 12 FALL 2009 BUSINESS STATISTICS 41000 7.4. Simple Time Series Plot 1. For a simple time series plot, go to the TIME SERIES PLOT submenu, and choose simple from the dialog box. 2. The following dialog box appears. Choose the variables to be plotted and click OK. 3. Minitab produces a plot as follows. GUIDE TO MINITAB 15 13 FALL 2009 BUSINESS STATISTICS 41000 8. Basic Statistics for pairs of variables In order to calculate basic statistics for pairs of variables, like covariance and correlation, go to STAT -> BASIC STATISTICS In this document examples of statistics are calculated assuming only two variables are being analyzed, however pair wise statistics for more than two variables can be calculated by simply adding all the desired variables to the “VARIABLES” box in the dialog windows. 8.1. Covariance 1. Choose COVARIANCE to obtain the following dialog box. Pick the pair of variables you wish to analyze and click OK. 2. The result will be presented in the Session window as presented below. GUIDE TO MINITAB 15 14 FALL 2009 BUSINESS STATISTICS 41000 8.2. Correlation 1. Choose CORRELATION and obtain the following dialog box. Choose the pair of variables to be analyzed. 2. Results are displayed in the Session window as presented below. 9. Doing Calculations with variables Minitab allows you to do calculations with the variables that you are using. For example you can add and multiply variables. In order to do these calculations you should go to CALC -> CALCULATOR GUIDE TO MINITAB 15 15 FALL 2009 BUSINESS STATISTICS 41000 The following dialog box appears This is basically a calculator that allows doing many calculations with the variables. Basic functions are found in the number pad and more sophisticated ones are found in the functions box to the right of the number pad. To make sure that your results is not overwriting a variable, name a new variable in the “STORE RESULTS IN VAVRIABLE” field in the top of the calculator. 9.1. Adding variables 1. To add variables name the variable where you want to store the results. 2. Select the first variable, press the “+” sign and select the second variable (and so on for more than two variables). You should obtain something similar to the window in the right 3. The result will then be shown in the worksheet window GUIDE TO MINITAB 15 16 FALL 2009 BUSINESS STATISTICS 41000 9.2. Taking logarithms Another useful function in statistical analysis is to take logs of variables. 1. Look for the “NATURAL LOG” or “LOG BASE 10” (depending on the one you need) in the function list. A shortcut to finding the functions is to choose “LOGARITHM” from the function drop down menu. 2. Inside the parenthesis, change number for the variable name. Highlighting “NUMBER” and hten selecting the variable you want to modify does this. 3. Make sure that you have defined a variable where you want to store results, by putting the name in the “STORE RESULT IN VARIABLE” box. 4. The result will appear in the worksheet window. 9.3. Logical functions Some statistical analysis will need to separate by groups according to characteristics that are contained in the data. Logical functions are particularly useful in these cases. A simple example on how to use them is described below. GUIDE TO MINITAB 15 17 FALL 2009 BUSINESS STATISTICS 41000 1. Choose the variable you want to do the logical test to. Here we are looking at the “SEX” variable. 2. Choose the logical test you want to use. Here we want to see which observations have the variable “SEX” equal 1. That is, which observations are males. 3. Make sure that you have indicated a variable in which to store your results, by typing the name of your result variable in the “STORE RESULT IN VARIABLE” box. 4. The result variable will be a binary variable (variable of 1s and 0s) where 1 indicates the logical test is true and 0 the test is false. The result variable will appear in the Worksheet window. 10. Using Minitab commands in the Session Window Minitab commands can only be written after the “MTB>” prompt. If this prompt is not visible in your Session Window, you need to enable commands, see section 3.2.3. 10.1. Minitab command language For Minitab to understand the commands you are typing you need to have in mind the following conventions, otherwise Minitab will not produce results. 1. Variable names must go inside ‘ ‘. This means that is you are referring to a variable named AGE you will need to type ‘AGE’ every time you are referring to it in a command line. 2. When you are referring to the number of a column you don’t need to type ‘ ‘. For example if you are using variable C1, you will only need to type C1. 3. Before doing a variable calculation you must type GUIDE TO MINITAB 15 18 FALL 2009 BUSINESS STATISTICS 41000 Let variable_name = In the variable_name field you can either use the number of the column or the name of the variable. 4. Whenever you are using a character or group of characters you need to use ‘ ‘. For example if you want to name variable C1 as AGE you need to write “AGE”. 10.1.1. Help with Minitab Commands 1. If you need help with the Session Command window or Commands go to 2. HELP -> HELP (See section 2.3) 3. Then under REFERENCES click SESSION COMMANDS, then SESSION COMMAND HELP. 4. Click on the link SESSION COMMAND HELP that appears on the right hand side window 5. The following window appears. There you can find functions and general help for Minitab Commands GUIDE TO MINITAB 15 19 FALL 2009 BUSINESS STATISTICS 41000 10.2. Examples 10.2.1. Adding variables 1. To add variables type in the command window Let RESULT_VARIABLE = VARIABLE1_NAME + VARIABLE2_NAME Suppose you want the variable test to be equal to age + sex, then you must type Let ‘test’ = ‘age’ + ‘sex’ 2. Results will appear on the worksheet window in the test column. 10.2.2. Naming a variable 1. Type in the session window Name COLUMN_NUMBER “NAME” Suppose that you want to name test column C8 then you need to type Name C8 ‘test’ 2. Results will appear in the worksheet. 10.2.3. Taking logs 1. To take (natural) logarithms of a variable type Let RESULT_VARIABLE = LN(VARIABLE_NAME) Suppose you want to have (natural) logarithms of age stored in column C9. Then you must type GUIDE TO MINITAB 15 20 FALL 2009 BUSINESS STATISTICS 41000 Let C9 = LN(‘age’) 2. Results will be shown in the worksheet window 11. REFERENCES 1. Minitab. Meet Minitab 15. 2007 2. Federico Bandi. Introduction to Minitab. Summer 2009. GUIDE TO MINITAB 15 21