Getting started with Minitab 14 for Windows

Transcription

1 INFORMATION SYSTEMS SERVICES Getting started with Minitab 14 for Windows This document provides an introduction to the Minitab (Version 14) statistical package. AUTHOR: Information Systems Services, University of DATE: November 2004 EDITION: 2.0 TUT 76 UNIVERSITY OF LEEDS

2 Contents 1 Introduction Aim of this Document Prerequisites Example Files The Minitab Environment The Project Manager Issuing Commands The Menu Bar The Toolbars Dialog Boxes Session Commands The Help System Projects Opening a project and its parts Saving a project and its parts Minitab Data Working with Data Missing Values Task 1 Entering Data in the Data Editor Task 2 Descriptive Statistics Task 3 Recoding Variables Task 4 Creating a Histogram Task 5 Editing a Graph Printing...22 Task 6 Using the Report Editor Task 7 Quitting Minitab Format Conventions In this document the following format conventions are used: Menu items are given in a Bold, Arial font. Keys that you press are enclosed in angle brackets. Windows Applications <Enter> Feedback: If you notice any mistakes in this document please contact the Information Officer. should be sent to the address infoofficer@leeds.ac.uk Copyright: This document is copyright University of Leeds. Permission to use material in this document should be obtained from the Information Officer ( should be sent to the address info-officer@leeds.ac.uk) Print Record: This document was printed on 15-Dec-04. 1

3 1 Introduction Minitab is an easy-to-use, flexible yet powerful package, for use on personal computers, which performs a wide range of statistical analyses. It is especially suitable for students and researchers who are not familiar with using a computer. The number of worksheets that can be opened at one time is only limited by the computer s memory. By default it can handle 100,000 cells or data items, some of which may be missing values. Data may either be entered via the PC s keyboard or retrieved from a file on disk, and may then be modified, transformed and saved on file from within Minitab. Printed copies of results appearing on the screen may be produced for examination at leisure. Minitab is largely self-documenting through its help facility, so that only a minimum of preparation is needed in order to use the package. 1.1 Aim of this Document This document provides an introduction to using the Minitab statistics package (version 14) for first-time users. The document describes the Minitab Environment and explains the basic features of the package. 1.2 Prerequisites This document assumes that you are familiar with the use of Microsoft Windows applications and logging on to the ISS Desktop. If you are not, please consult the document BEG 18 Getting Started With Microsoft Windows. It is also assumes that you are familiar with basic statistical terminology Example Files To download the example files: open a web browser such as Internet Explorer and go to URL: Scroll down to TUT76 - Getting started with Minitab for Windows and right-click on the Pulse.MTW. Select Save Link Target As When the Save As dialog box appears, select a suitable directory and click Save. 1.3 The Minitab Environment When Minitab starts, a new project is opened automatically, and three windows will be visible: Data window Session window Project Manager (minimised at startup) The project file contains worksheets that contain the data, data windows that display the data, a session window that contains the results of analysis, graphs created with Minitab s Graph command, toolbars for issuing commands, a status bar and a Project Manager. Many windows may be displayed, but only one of them will be active. The active window will show three asterisks next to the title. 1

4 Figure 1 Active Data Window The windows can be accessed from the Window menu, by clicking on their title bar or using the appropriate shortcut keys: Window Shortcut Note Data <Ctrl + D> Session <Ctrl + M> Project Manager <Ctrl + I> Command Line Editor <Ctrl + L> See section The Project Manager This contains a series of folders: Folder Session History Graphs Report Pad Related Documents Worksheets Purpose Management of session window output Stores a list of commands generated in the current session Management of graphs Creating and editing reports of Minitab work Contains project related, non Minitab files Stores individual folders for any open worksheets. Each of these displays a summary of the data used in the worksheet Figure 2 The Project Manager Window (Report Folder Selected) 2

5 1.3.2 Issuing Commands There are three ways of accessing Minitab commands: through the menus; through the toolbar; or using session commands. However a command is issued, it always acts on the data in the current worksheet, i.e. the active Data window. To make a window active, click on it or choose it from the Window menu The Menu Bar This gives access to all the Minitab commands. Figure 3 The Menu Bar To run a command from the menu bar, click on the menu to open a submenu and then select the required commands. The main menus are: Menu Item File Edit Data Calc Stat Graph Editor Tools Window Function Open, save and print and close projects and their components. Cut, Copy and Paste commands, access to the Command Line Editor and links to external documents. Commands to manipulate worksheet, such as Merge Worksheets, Sort, Split and Change Data Type. Commands to calculate mathematical expressions and transformations, generate datasets, calculate row and column statistics and manipulate matrices. This menu contains all the statistical commands. Commands to generate and modify a wide variety of graphs. Items in the Editor menu depend on which window is currently active. For example, when the Data window is active it contains commands to format data and insert rows or columns. Allows access to Windows Explorer, Microsoft calculator, notepad and selection of the Minitab toolbars. It also contains hyperlinks to the Minitab knowledge base, and allows the user to customise the Minitab interface. Selects a new active window and alters the way the windows and other items are displayed. Shortcut Key <ALT + F> <ALT + E> <ALT + A> <ALT + C> <ALT + S> <ALT + G> <ALT + D> <ALT + T> <ALT + W> Help Help items. These will be described section <ALT + H> 3

6 1.3.4 The Toolbars These provide access to the most commonly used functions. If a toolbar is not currently displayed, click Tools > Toolbars and then select the appropriate one. Repeat this process to hide a toolbar. Alternatively, rightclick the mouse to switch the toolbar on or off. The commands available on a toolbar depend on the active window. Pointing the mouse cursor at a button on a toolbar will cause its function to be displayed. The Project Manager toolbar provides shortcuts to all the Project Manager folders. Figure 4 Toolbars 4

7 1.3.5 Dialog Boxes Many commands will generate dialog boxes. Minitab dialog boxes will often have a variable list box, which displays columns, stored constants or matrices. When a text box requires a variable, select one from the list of all valid variables in the current worksheet and double-click on it to fill the text box. (Alternatively, click once to select it and then click the Select button.) Figure 5 Dialog box with Height variable selected Session Commands Experienced Minitab users may wish to use the command style. Commands can be typed either into the Command Line Editor or into the session window. To use the Command Line Editor, select Edit > Command Line Editor (<Ctrl + L>) from the menu. This will open a new window, into which the commands can be typed. To enter commands in the Session window choose Editor > Enable Commands from the menu. The MTB> prompt will then appear in the Session window. When the MTB> prompt is present, any analysis carried out using menus and dialog boxes will result in the corresponding commands being recorded in the Session window. The session window may then be saved as a separate file to be reused at a later date. For more information about the Minitab command language choose Help > Session Command Help from the menu. 5

8 1.3.7 The Help System A comprehensive help system is available from the Help menu, and the Help files are in a printable format. In addition to complete menu and dialog box documentation, there are overviews, examples, guidance for setting up your data, information on calculations and methods, and a glossary. Item How to use Help StatGuide Tutorials Session Command Macros Minitab on the Web Keyboard Map About Minitab Meet Minitab Description Explains the organisation of the help system. Provides statistical guidance for interpreting statistical tables and graphs in a simple, practical way. These step-by-step tutorials introduce the Minitab environment and provide a quick overview of some of Minitab s most important features. Each tutorial is designed to explain the fundamentals of using Minitab, e.g. how to use the menus and dialog boxes, how to manage and manipulate data and files, how to produce graphs. There are five tutorials: Graphing Data, Entering and Exploring Data, Analyzing Data, Assessing Quality, Designing an Experiment. Sample files are available for use with these. This provides information and the command syntax for all session commands, indexed alphabetically and by function. Illustrates how to use the commands and describes the different types, rules to follow, formats and capabilities. Contains a list of macros arranged by function. Contains a hyperlink to Minitab s website: Has a list of all the shortcut keystrokes that can be used in place of menu commands. Contains the product name, release number, serial number, contact details and system information. Documentation can be downloaded in PDF format from Note: Further online resources and downloads are available from Other Minitab documentation, including the Minitab Reference Guide and the Minitab User guide, is available from the ISS Help Desk. 6

9 2 Projects An empty project is created automatically when Minitab is started. A Minitab project consists of all parts of your work, including the text output (session window) from the commands issued, the data stored in worksheets (viewed in the data windows) and any graphs that have been created. Projects can be opened and saved as a whole, or individual parts of a project can be saved separately. Items, such as a worksheet or graph, can also be discarded from a project. 2.1 Opening a project and its parts Type Instruction Notes project File > Open Project or press <Ctrl+O> worksheet File > Open Worksheet Available file types for data are: Excel, Quattro Pro, Lotus 1-2-3, and dbase files. For MS Windows programs, DDE (dynamic data exchange) can be used to import data into Minitab. worksheet File > Other Files > Import If the data required are not from these applications, save the data in a text file. Most applications can create text files. Minitab can open plain text (ASCII) files, which usually have an extension of TXT (for text) or DAT (for data). worksheet graph File > Query Database (ODBC) File > Open Graph If the other application is a database, then ODBC can be used. It may be necessary to include a new data source if the required on is not present in the Select data Source dialog box. Note: When a worksheet or graph is opened, the data are copied to the open project. Any changes made to the worksheet or graph are not automatically saved to the worksheet or graph file, even if the project is saved. To save changes to the individual files, save the worksheet or graph separately. 7

10 2.2 Saving a project and its parts To save a project, choose File > Save Project As from the menu. Type in a filename in the File name: box and choose a suitable directory to store the file in and click Save. The first time a file is saved, choosing File > Save Project from the menu (or pressing CTRL+S) has the same effect as using File > Save Project As Once the project has been named, using File > Save Project will automatically overwrite the existing file without requiring entry of a file name. To save the individual parts of a project choose: Type Instruction Notes Project Worksheet Session Window Graph History file File > Save Project As File > Save Current Worksheet As File > Save Session Window As File > Save Graph As Minitab Project (MPJ) Available file types are: Minitab worksheet (MTW), Minitab 12, 11, or 10 worksheet (MTW), Portable worksheet (MTP), Text file (DAT, TXT), Excel file (XLS), Lotus files (WK?), Quattro Pro file (WB1, WQ1), dbase/foxpro file (DBF), Web Page (HTML). Mintab Session (TXT), Rich Text Format (RTF), Web Page (HTML), List File (LIS). The default graph type is MGF (Minitab Graph). Other types are also available: JPEG (Joint Photographic Experts Group), TIFF (Tagged Image File Format), PNG (Portable Network Graphics), BMP (Windows Bitmap). For high quality printing, use EPS (encapsulated postscript). Note that an EPS file cannot be viewed in a word processor. TXT, MTJ Note: It is good practice to save a worksheet as a separate file, so that it will be stored safely even if the project is corrupted. 8

11 3 Minitab Data In Minitab, data are contained in a worksheet. This looks similar in appearance to a spreadsheet, but in Minitab cells do not contain formulae that update results automatically. If a calculated variable is created from existing variables, and then the value of one of those variables is updated, the value of the calculated variable will not be updated automatically. A Minitab project may contain several worksheets. Rows in the worksheet represent cases. Columns represent attributes of the cases and are known as variables. Quantitative variables are measured on an ordinal, interval, or ratio scale; for example, measuring heights and weights. Qualitative (categorical) variables are measured on a nominal scale; for example gender or machine number. During an experiment, independent variables or factors are set by the experimenter; while dependent variables are observed and measured. There are three types of data: Numeric numbers Text text, numbers, spaces or special characters Date / Time dates e.g.1/1/04, times e.g. 10:20:30AM or both Note: Although dates can be formatted in a variety of ways, Minitab stores them internally as numbers and so they can be used in calculations. Data can take three forms: Column Constant Matrix Columns may consist of numbers, text or date / time data. A column can be referred to either by the letter C followed by a number, e.g. C1 or by a variable name. Constants may contain a single number or a text string e.g. Paris. A constant can be referred to either by the letter K followed by a number, e.g. K22, or by a variable name. Matrices contain a rectangular block of numbers, and may be referred to either by the letter M followed by a number, or by a variable name. The following restrictions apply to variable names: The length may not exceed 31 characters They must not begin or end with a blank They must not include the symbol ' or # They may not begin with, or consist entirely of, the symbol * They must not be repeated: the same name cannot be used for two variables (columns, stored constants or matrices) in the same worksheet 9

12 3.1 Working with Data Three windows can be used to work with data: the Data window, the Worksheet folder and the Session window. The Data Window contains columns of data that are in the worksheet. If multiple worksheets are open, each has its own data window, where the data can be viewed, edited or manipulated. Figure 6 The Data Window The Worksheet Folder in the Project Manager summarises the columns, stored constants and matrices in the current worksheet. Figure 7 The Worksheet Folder 10

13 The Session Window can be used to display the columns, constants and matrices. The command Data > Display Data will open a dialog box. Figure 8 Display Data Dialog Box In Figure 8, the columns id and gender have been selected. (To select a variable, click on its name in the left hand column and then click the Select button.) Clicking on OK in the Display Data dialog box will cause the variable values to be displayed in the session window. Figure 9 Session Window showing id and gender Variables Note: If the MTB> prompt is on, typing the command Print id, gender in the session window will achieve this result. 11

14 3.2 Missing Values In circumstances where information about a variable has not been collected for any reason, the data item is said to be a missing value. The code for this is * if the item is numeric, and a blank field if it is alphanumeric (text). Most commands exclude from analysis all rows with a missing value and display the number of excluded points. When an arithmetic command operates on a missing value, Minitab sets the result to *. Note: When * is entered as a value in the Data window it should not be enclosed in quotation marks. However, the * must be enclosed in quotation marks when it is part of the command line typed at the MTB> prompt. Task 1 Entering Data in the Data Editor Activity 1.1 Run Minitab by clicking Start > Programs > Statistics > Minitab14. When Minitab opens, the session window and an empty worksheet will be displayed. If the command prompt MTB> is not showing in the session window, select Editor > Enable Commands. If the direction arrow in the session window is pointing downwards, click once on it to change the direction to right. (When the direction arrow points downwards, the effect of pressing the <Enter> key is to move the cursor down to the cell below the current one. Normally data are entered by case). Figure 10 The Direction Arrow Pointing Right Activity 1.2 Enter the values Centre, Order, Arrival, Distance in the row immediately under that which contains variable numbers. After each name is entered, press the <TAB> key to move to the next column. After the last value, type <Ctrl + Enter> to move to the next row. Enter the dataset shown below: Figure 11 Sample Input Data 12

15 When you have completed this task, the worksheet should resemble the one shown in Figure 12. Figure 12 Completed Worksheet Note that the variable number for Centre has changed to C1-T to show that it is a text variable, the variable numbers for Order and Arrival have changed to C2-D and C3-D respectively to show that they are date variables, and the variable name C4 is unchanged because it is a numeric variable. Note also that where gaps were left in the data, Minitab has inserted asterisks to indicate missing values. Activity 1.3 The entry for the distance variable in the second case is incorrect, and should show a value of 309. Correct it by selecting the cell and typing the value 309. Activity 1.4 Select File > Save Current Worksheet As and name it Orders. Click <Save>. Note that you will select a folder of your own, and so the contents of the screen that you see may differ from this. Figure 13 Save Worksheet Dialog Box 13

16 Activity 1.5 Now the project should be saved. Select File > Save Project As and name the project Tutorial. Minitab will append the file extension MPJ automatically. Once the project has been saved in this way, it will only be necessary to click on the SAVE icon on the standard toolbar in order to save it again. Activity 1.6 It would be useful to calculate a new variable to show delivery times. Select Calc > Calculator from the menu and then complete the dialog box as shown below. First enter the name of the new variable DeliveryTime. Click on the variable Arrival and then click Select. Click on the minus sign in the calculator. Click on the variable Order and then click Select. Finally, click OK. (Note that a slightly shorter way of selecting variable names is to double-click on them.) Figure 14 The Calculator Activity 1.7 In Activities , the graphical interface was used to perform a variety of tasks. Because we enabled commands before we began, the corresponding code that Minitab created in order to execute the tasks has been printed in the session window. Figure 15 Minitab Command Language Statements 14

17 Task 2 Descriptive Statistics Activity 2.1 This time an existing file will be used. Click File > Open Worksheet, and navigate to the directory in which you saved the data files for this tutorial. Select the file Pulse.MTW. This file will now be displayed in another data window. It may be necessary to rearrange the windows in order to view all of its contents. The previous worksheet is still open, and by dragging the windows it will be possible to see both. Note that only one of the windows is the active window. The active window is the one which has three asterisks after its title. Figure 16 Active Worksheet Pulse.MTW Activity 2.2 From the menu, select Stat > Basic Statistics > Display Descriptive Statistics. Figure 17 Stat Menu showing Basic Statistics Sub-menu 15

18 Activity 2.3 Double-click the variables Height and Weight to select them. Click the Statistics button to display the available statistics and then click OK in both dialog boxes. Figure 18 Display Descriptive Statistics Dialog Box The results will be displayed in the session window. Figure 19 Results of Analysis Activity 2.4 Scroll upwards in the session window to see the commands that have been executed as a result of the menu selections. 16

19 Task 3 Recoding Variables Activity 3.1 The variable Sex is a numeric variable which uses the code 1 for male and 2 for female. A new variable, Gender will be created by recoding this variable. Click Data > Code and select Numeric to Text from the sub-menu. Figure 20 Data Menu Activity 3.2 Complete the next dialog box as shown below. Note that when this first appears, the left hand panel shows a list of variables in the current worksheet. Click OK and the new variable Gender will be added to the worksheet as C9-T. Figure 21 Numeric to Text Dialog Box 17

20 Task 4 Creating a Histogram Activity 4.1 A histogram of the variable Height will now be created, with separate panes for the groups male and female. Select Graph > Histogram from the menu. Choose the option With Fit and click OK. Figure 22 Histogram Dialog Box Activity 4.2 Double-click the variable Height in the left-hand panel to select it and then click the Multiple Graphs button. Figure 23 Variable Selection Box for Histogram 18

21 Activity 4.3 At the next dialog box, click the By Variables tab, and then doubleclick the variable Gender. (Alternatively click once on Gender and then click the Select button.) Figure 24 Multiple Graphs Dialog Box Click OK at both dialog boxes and the histogram will be displayed as a separate graph window. Figure 25 Graph Window 19

22 Task 5 Editing a Graph Activity 5.1 In order to edit a Minitab graph, it is necessary to double-click the area or object that is to be modified. Double-click the title of the histogram to display the Edit Title dialog box, make the modifications shown below and click OK. Figure 26 Edit Title Dialog Box Activity 5.2 Now double-click the white panel area around the graph to produce the required dialog box, and change the background colour. Click OK. Figure 27 Edit Data Region Dialog Box 20

23 Activity 5.3 Double-click on the Normal Distribution line to open the Edit Distribution Fit dialog box. Make changes to the colour and thickness of the line. Double-click the bars to open the Edit Bars dialog box, and make changes to the pattern and colour of the bars. Activity 5.4 Experiment with editing the other areas of the chart. Other options include: Edit Footnote, Edit Axis Label, Edit Table, Edit Graph and Figure Regions, Edit Bars, Edit Panels and Edit Scale. An example of an edited chart is shown below. Figure 28 Edited Histogram Activity 5.5 This chart can now be saved for later use. A variety of graphics formats is available. If the chart is to be used for a web page, a suitable file format would be JPEG or PNG. Make sure that the chart is selected, or the required option will not be available on the File Menu. Click File > Save Graph As Select the arrow to the right of the Files of Type box and choose JPEG. If necessary, give the chart a different name and then click Save. 21

24 4 Printing The contents of any Minitab window can be printed. To print a window, select it by clicking on it or selecting it from the Windows menu. An option to print that window will now be available under the File menu. For example, to print a worksheet: Select the appropriate data window and choose File > Print Worksheet (or CTRL+P). Choose the options required to format the printed output and click on OK. The standard Windows Print dialog box is displayed. Ensure that the correct printer has been selected in the Printer Name box and click OK to print the window. Depending on the active window, the following options will be available on the File menu: Print Session Window Print Graph Print Worksheet Print Report Window Print History Window Note that the session window contains limited formatting. If required, its contents may be copied and pasted into a Word Processor, where formatting can be applied. Minitab does have a Report Editor, which allows formatting. Results may be copied from the session window into the Report Editor, formatted, and then printed. Task 6 Using the Report Editor Activity 6.1 Scroll upwards in the session window until the results of the descriptive statistics are displayed. Select the output and click Edit > Copy. Maximise the Project Manager Window and double-click Report Pad. Click in the right hand panel and select Edit > Paste. The results will appear in the report, and they can now be edited. Figure 29 Project Manager showing Report Pad open 22

25 Activity 6.2 Select the title text and right click the mouse. From the context sensitive shortcut menu, select Centre. Repeat this process to change the font size and colour. Figure 30 Shortcut Menu Activity 6.3 Minimise the Project Manager window, and select the chart. Click Edit > Copy Graph, and then maximise the Project Manager window. Click in the report pad window and select Edit > Paste. The chart will now be displayed. Activity 6.4 With the report pad selected, click File > Save Report As Choose either RTF (rich text format) or HTML (hypertext markup language), give the file a name and click on Save. Activity 6.5 Select File > Print Report Pad. 23

26 Task 7 Quitting Minitab You should always quit any computer program when you have finished your session. Never switch off the computer without closing down Windows. Do not leave a computer whilst you are still logged on to it as others may use your account and could damage your files. Activity 7.1 Before leaving Minitab make sure you have saved the components of your work (see Section 2.2). To leave Minitab choose File > Exit or click on the Close box in the top right-hand corner of the Minitab window. If you have made any changes since you last saved your work, you are asked if you want to save changes to your project before closing. Select Yes to save the project, No to exit without saving, or Cancel to return to Minitab without saving Activity 7.2 After leaving Minitab, choose Start > Logout. You must always logout before leaving your computer. 24