SPSS - General Considerations

INTRODUCTION TO SPSS

Introduction. This material is appropriate for SPSS Windows Version 13. Before moving ahead to solve problems using SPSS, it is useful to first consider some features and procedures of SPSS that you might want to use regardless of the problem you are solving. We will try to be brief because we know this kind of material can be boring, and we know you can’t wait to experience the excitement and fun that accompanies analyzing data with SPSS. Nonetheless, this is the best place to talk about these common elements. If it turns out that you want to learn about SPSS in more detail than presented here, I recommend reading L. A. Kirkpatrick and B. C. Feeney, A Simple Guide to SPSS for Windows for Version 12.0 & 13.0, Wadsworth, Belmont, CA, 2006. If you have a question concerning something I have not covered, it is also worth consulting the Help function that SPSS offers on the menu bar at the top right of the two windows it displays, the Data Editor window and the Viewer window.

In much of the material that follows, you will be learning how to use SPSS by interacting directly with SPSS opened on your own computer. There are two ways for you to do this. The first is to print the instructional material and refer to it as you interact with SPSS on your computer. In this method, you will always be in SPSS, ready to input to it as the instructional material you have on hard copy directs. The instructional material will be displayed on screen by the web browser in Microsoft Word files. To print the instructional material displayed on screen, simply click File > Print as you would to print any Word file. The second method assumes that you have both SPSS and the SPSS instruction active on your computer, and that you toggle between the two. The way to toggle is to press Alt+Tab once (hold the Alt key down, press Tab once, then release both keys). Pressing Alt+Tab once causes the computer to revert to the previously used application. Thus if you are currently in the active SPSS application and had just previously been running the SPSS instructional application, when you press Alt-Tab once, the computer will switch back to the SPSS instructional application, and vice versa.

Basic Steps in Analyzing Data. Using SPSS makes data analysis very easy. All that you need to do is:

Enter the data into SPSS. The two most common methods are to enter the data by typing it directly into the Data Editor; or to open a previously saved SPSS data file that resides on your computer into the Data Editor. For this instructional material, we have introduced a third method. We have saved all of the SPSS data files on our web server. The third method allows you to download the data file from our web server for any example or problem used in this instruction directly into the Data Editor.

Select a procedure. Select a statistical analysis or graphing procedure from the menus at the top of the Data Editor or Viewer to analyze the data or to construct a graph.

Interact with one or more dialog box(es). Selecting a procedure produces one of more dialog boxes. Input from you to the dialog box(es) fills in the appropriate details for the procedure to correctly act on your data.

Run the procedure and view the results. Once the details are entered in the dialog box(es), clicking OK gives SPSS the go-ahead and causes the procedure to be carried out. The results are displayed in the Viewer.

SPSS Windows. As mentioned previously, SPSS has two windows, the Data Editor window and the Viewer window. The Data Editor window displays the Data Editor. The Viewer window displays the output from the Data Editor. You can move from one to the other by clicking Window on the menu bar at the top of either window and then clicking either SPSS Data Editor or SPSS Viewer as appropriate.

Data Editor. When you first open SPSS, the Data Editor will appear on screen (you will be in the Data Editor window). The Data Editor is where you enter, edit, save and print the data. The Data Editor also allows you to select and run procedures for analyzing and graphing the data. The results of analyzing or graphing the data are output from the Data Editor to the Viewer. The Data Editor is presented at start-up because the first thing you will do to solve a problem or analyze the data from an experiment with SPSS is to enter the data and specify variable information, such as the variable(s) name(s). Once the data is entered, analysis or graphing can be carried out and the results sent to the Viewer for your consideration.

The Data Editor has two possible views, the Data View and the Variable View. When you first open SPSS, the screen will present either the Data View or the Variable View. Let’s discuss the Data View first.

Data View. Figure Intro.1 shows the Data Editor displaying the Data View. The Data View is composed of a data table and a menu bar for performing various procedures and for getting help if desired. When you first open SPSS or obtain a new data table, the table will be blank. Note the menu bar at the top of the figure and the blank data table. There is a tool bar under the menu bar that allows procedures to be selected by clicking icons instead of using the menu bar. Most of our discussion will proceed via menus rather than using the tool bar.

Figure Intro.1. The Data View at start-up.

Figure Intro.2 shows the Data View of an untitled Data Editor in which I have entered the scores of 10.00, 12.00, 15.00, 23.00, 18.00, 31.00, 40.00,16.00, 28.00, and 36.00 for a variable named X, and 7.00, 9.00, 4.00, 14.00, 21.00, 15.00, 10.00,13.00, 18.00, and 5.00 for the variable named Y. I will show you how to enter data and name variables a little latter in this section.

From this figure, you can see that the Data View shows a table where each column pertains to a variable. In columns that contain data, each column displays the variable name and under the variable name, the values for that variable. These variables and values could be ones from an experiment you have conducted or from a homework problem. At the top of the screen, there is a menu bar that permits data entry, editing, saving and printing, procedure selection (transforming the data, analyzing the data, graphing the data, etc), and getting help should you have questions. We will discuss some of these functions a little later in this general section, and the rest as appropriate in conjunction with data from specific experiments or problems. I hope you will like and be excited by how easily, quickly, accurately and esthetically you can accomplish these functions using SPSS.

Figure Intro.2. The Data View showing two variables, X and Y, and the values of each variable.

Variable View. The Variable View of the Data Editor is shown in Figure Intro.3. It is obtained by clicking the Variable View tab at the bottom left of the Data View. Clicking the Data View tab when the screen is displaying the Variable View will produce the Data View. Like the Data View, the Variable View displays a table; only in this table each row represents a variable, giving its name and other important information about the variable. As with the Data View table, when you open SPSS or obtain a new data table, the table presented in the Variable View is blank. When you enter numeric data into the Data View, SPSS gives the data a variable name and assumes the variable is a numeric variable. You can also give the variables names of your own choosing. Generally, it is better to name the variables yourself. We will explain why in a later section. In the table displayed in Figure Intro.3, I have entered the names of two variables, X, and Y. The remaining entries shown are the default entries that SPSS gives to each numeric variable.

Figure Intro.3. The Variable View showing the names of two variables, X and Y, along with other information concerning each variable.

Entering Data by Typing Directly into the Data Editor. Data is entered via the Data Editor, Data View. Let’s assume that you have the following IQ scores that you desire to enter.

IQ: 100, 105, 118, 120, 123.

We will further assume that you have just opened SPSS, that you have a blank Data Editor, Data View on screen, and the highlighted cell is the upper left cell (intersection of row 1and the 1st column). Now, please open SPSS on your computer, and verify that the display is as assumed. Next enter the data into your Data Editor as instructed below.

The display on your computer should look like that shown in Figure Intro.4.

Figure Intro.4. Five scores entered into the Data Editor

When you enter data into the Data Editor, SPSS automatically gives the variable a name. The first variable gets the name, VAR00001. The next variable would get the name VAR00002, etc. As mentioned earlier, it is often better to assign your own name. Assigning your own name often makes the output more meaningful and helps navigate dialog boxes when there are multiple variables. Let’s now assign our own name by changing VAR00001 to IQ. To do so:

The display on your computer should now look like Figure Intro.5.

Figure Intro.5. Variable View with IQ entered as the variable name.

Note that when you change the name of a variable in the Variable View screen, that name change is carried through in the Data View table as well. Figure Intro.6 shows the Data View. Note the name of the variable is now IQ. Compare your Data View with Figure Intro.6 by

Figure Intro.6. Data View showing the scores with IQ as the variable name.

Variable names. Variable names must begin with a letter. The rest of the characters can be any letter, any digit, a period, or the symbols _, @, #, or $. Variable names cannot exceed 64 characters and cannot end with a period. Typically, variable names do not exceed 8-10 characters.

Saving Data Files. It is a good idea when you have finished entering the data and naming the variable to save the data file. This is because any changes to data files made in a session, including initial data input, only last as long as the session, unless you save the file. Let’s assume you have just entered the data shown in Figure Intro.6 and the variable has been named IQ, and that you are in the Data View. Let’s assume further that we wish to save this file under the name, IQexp (exp standing for experiment). You don’t need to add the extension .sav because SPSS does this automatically. To save this file on your computer with the name IQexp, do the following:

Figure Intro.7. : Save Data As dialog box.

Figure Intro.8. Data View showing the file name IQexp.sav in the title bar at the top left of the screen.

The default for file type on the Save Data As dialog box is appropriate for saving SPSS data files in a format such that SPSS will read them. However, SPSS allows saving data in many other formats to be read by other applications such as Excel, etc., so be sure the Save as type: box has entered in it SPSS (*.sav) before clicking the Save button. This is the default, and is the correct extension for our use.

Printing a Data File. There are occasions when you may want to obtain hard copy of a data file. For instance, your instructor might want you to hand copies of the data files as part of a homework assignment. Let’s assume you want to print the data file IQexp.sav, that it is currently loaded into the Data Editor and you are in the Data View. To print this file,

Obtaining a New (Blank) Data Editor. When you have finished analyzing the data for one problem or experiment, and you want to move on to another problem, it will be necessary for you to enter the data of the new problem. If the Data Editor already contains a data file and you are going to type the new data directly into the Data Editor, it is useful to first obtain a new or blank Data Editor into which you can enter the new data. To illustrate how to do this, we will assume that you are in the Data Editor, displaying the Data View and you have a saved data file already entered in the data table. To obtain a new (blank) Data Editor,

Entering Data by Opening Saved Data Files that are Stored on Your Computer. We have already discussed entering Data by directly typing it into the Data Editor. Another way to enter data is by opening a saved data file stored on your computer into the Data Editor. To illustrate how to do so, let’s assume you have a blank Data Editor on screen. As you now know, this can be accomplished by obtaining a new Data Editor. It also occurs when you first open SPSS. Let’s further assume that you desire to enter the saved data file, IQexp.sav and that this file is stored on your computer. To do so,