Depending on the computer you find yourself in front of, here s what you ll need to do to open SPSS.

Transcription

1 1 SPSS 11.5 for Windows Introductory Assignment Material covered: Opening an existing SPSS data file, creating new data files, generating frequency distributions and descriptive statistics, obtaining printouts from SPSS. To start SPSS for windows Depending on the computer you find yourself in front of, here s what you ll need to do to open SPSS. 1. There may just be an SPSS icon on the desktop. If there is, double-click on it and that s all there it is. 2. If there s no SPSS icon on the desktop you may have to start the program using the Start button. Click on Start. Click Programs. Click Radford University Course Software. Click Math-Stats. Click SPSS 11.5 Click SPSS for Windows That ought to do it. At this point you ve got three basic options: (a) open an existing data file that has already been stored as an SPSS system file, (b) import a data file that is in another format (e.g., ascii, excel, SAS) into SPSS, or (c) enter new data into the SPSS spreadsheet to create a new data file. The diskette distributed in class should have a file already on it named bpdata.sav. Files with the extension.sav are SPSS system files (they are in a binary format that SPSS knows how to read). The data contained in the bpdata.sav file are described in a separate handout. To open an existing SPSS data file Now, we re going to have you open the bpdata.sav data file. Click file and go to open At the drives option, click a: You will see the filename bpdata. Click on the file bpdata and click ok The data have now been brought into the SPSS spreadsheet. The data are organized into rows and columns. Each row presents the data for a particular subject. SPSS refers to a row of data as a case. You ll have as many rows in your spreadsheet as you have subjects. Each column contains the data for a particular variable. The names for each of these variables appear at the top of the columns. In my data files I

2 2 always have a variable that contains an identification number for each subject (subid). Now that the data are in the spreadsheet we re in a position to do something useful with them. SPSS for Windows makes it very easy to get statistical types of jobs done. The basic idea in using SPSS is that we can use pull-down menus to select the type of operation you want done. You click on that option and a separate window pops up that guides you through the process of telling SPSS exactly what you d like it to do. There s not very much you have to remember on your own. All you have to do is (1) know what you want (that s the hardest part), (2) click on the appropriate set of options, and then (3) know how to find the information you need in the output that SPSS gives you. Very quickly, let s take a look at how to get SPSS to give you descriptive information about the variables you re working with. To generate a frequency distribution Click the Analyze pull-down menu. You should now see various options that SPSS provides for data analysis. go to Descriptive Statistics click Frequencies highlight a variable you want to examine and click the arrow to move that variable to the variables box towards the right of the window. You can put as many variables as you want in this box. Go ahead and select the variables age and traitan1. click the statistics option click in the boxes for the measures you d like to get descriptive statistics on. Here, try checking the mean, median, and standard deviation options. click continue click the charts option click the histograms option click the With normal curve option. This will provide an overlay of a normal distribution on top of the frequency distribution for the variable being graphed. This provides a convenient way to get a sense of how close the distribution for that variables comes to that of a normal distribution. click continue Back at the main frequencies menu, click OK Working with an output window The program will now present you with an output window. The top of each section of output always contains a title. In this case the title is Frequencies. You can change this title to whatever you want. To change the title,

3 3 double-click anywhere within the existing title. You ll see a box with dashed lines appear around the existing title and a blinking cursor at the start of the box. At this point you can delete any of the original text you want and put in a title that makes sense to you. When you re working on your own analyses you ll want to put in titles that make it clear what information is contained in this section of output; for example here we might put Frequency distributions for age and trait anxiety, all subjects. Titles make it much easier to make sense out of printouts of your output when you go back to them weeks or months later. The left window provides you with an outline of what is contained in the output. You should be seeing a branch for Frequencies and then branches from Frequencies that are labeled Title, Notes, Statistics, Stress, etc. Each of these branches represents a section of the output that SPSS has generated. You can go to a different section of the output window just by clicking on the branch for the section you want. You can hide or display any of these parts of the output by double-clicking on that row. Notice that branch labeled Notes has a closed book icon next to it. This indicates that this section of the output is not being currently displayed in the output window (the open book icon indicates that a section of output is currently being displayed). Go ahead and double-click on the notes branch. A section of output has opened up that provides some useful information about the procedure that SPSS has just executed. For example, it can tell you the date the job was run, whether the analysis was limited to a certain groups of subjects, and it gives you the SPSS syntax (command language) that corresponds to the options you selected within the windows version of the program. For example, the syntax frequencies variables = traitan1 age/statistics = stddev mean median represents the programming language that researchers used to have to submit to SPSS to get the same job done. Nowadays, you don t have to generate these programming lines yourself (SPSS does this for you), but after you get used to looking at these command lines they give you a very useful way of reminding yourself of what exactly you d asked SPSS to do for you. We ll talk about this later, but SPSS also provides a very easy way of storing these command lines so that later on, when you want to run the same job again, you can just re-submit a file that contains these same command lines. In other words, saving these command lines to a file is a way of saving your work so that you don t have to figure out how to do something all over again. The larger window on the right contains the output. You can move up or down through the output using the arrows at the left side of the window. Just for fun, double click on the histogram for age (i.e., bar graph). This will put the graph in a Chart Editor window that you can print the graph or save it to a separate document. The Chart Editor also allows you change many aspects of the graph, such as the title, axis labels, the number of intervals in the frequency distribution, and so on. One particularly interesting thing to look at is what happens when you change the number of intervals in the histograph. To do this Double click on the values on the X-axis. You should get an Interval Axis window

4 4 Under Intervals, click custom Click define Change the number of intervals to several different values and see if this changes the shape of the frequency distribution. Notice that the statistics you asked for are located just to the right of the graph. When you get a chance, try clicking on different parts of the graph to get a sense of how to alter the appearance of the graph. Go ahead and minimize the Chart Window to get back to the Output Window. The minimize button is at the top-left corner of the window. Just like in other Windows programs, the minimize button is the one on the left (the flat line). If you wanted to get rid of the chart you could just click the X and it would close this window. Saving an output window to a file You can easily save an output window to a file so that you can go back to it later. To do this you click File, then click Save as, then enter the filename you want and select the folder where you want the file to go. Printing the contents of an output window You can print all or any part of an output window. In the branching tree part of the output window (the left-hand side) highlight the section of the output you want to print (for example, to select the entire contents of the frequencies section, click on the frequencies branch). Now click File, click Print, and select the options you want in the Print window. If there s a section of output you don t want to print, simply double-click on its row in the branching tree diagram. This will eliminate it from the display on the righthand side of the output window and you ll get the closed book icon for that branch of the output. A good way to save paper is to use the Properties option when you enter the printer window. Here, you ve got the option to put 1, 2, 4, 6, or even 9 (with a magnifying glass) pages of output onto a single printed page. When I ask you to print stuff for class, try to use the 4 output pages per printed page option. Getting descriptive statistics If you want descriptive statistics, but don t want to have to wade through a bunch of frequency distribution tables, the descriptives window is a nice option. Click Analyze Click Descriptive Statistics Click Descriptives Highlight a variable you want you use and click on the arrow to put it in the Variable(s) window. You can do this with as many variables as you want.

5 5 Click the Options button Click the empty boxes next to the descriptive statistics that you want. Click continue, then OK The output for the descriptive statistics are added to the bottom of the existing output file. At this point, please minimize the Output Window to return to the SPSS Spreadsheet. Now we re going to leave the bpdata data file and have you type in the data for a new data file. To create a new data file using the SPSS spreadsheet Entering data in SPSS is easy. Each row contains data from one subject. Each column contains data from one variable. Let s say that we had a data set with data on four variables from 10 subjects. All of the subject are college students. These variables are the subject s ID number (ID), the IQ score for the subject (IQ), the subject s GPA (GPA), and the number of years the subject has been at college (Year). The data are presented below. ID IQ GPA Year If there is already a data file in the spreadsheet (like there probably is now), go to File and click New and then click Data. The program will ask you if the old data need to be saved to a file. Say yes if you want to save any changes that you might have made in the data set. At this point the old data set will disappear and all you should see is a blank spreadsheet. Move the cursor to the top-right cell in the spreadsheet and click once. That cell should now be highlighted with a thick black line around the outside of the cell. Now you can type in the number for the first variable for the first subject. Because the first variable in the data set is the person s ID number, this score will be 001. When you press the Enter key the number should show up in the spreadsheet and the next box down should be highlighted.

6 6 Entering a variable name A variable name in bold type is created at the top of the column, var To change this variable name, double-click on the variable name (you should now be in the Define Variable window) and replace the old name with something more meaningful. In the assignment the name for the first variable is ID (because it represents the subject s ID number). Specifying a Variable Label Now that you re in the Define Variable window, we might as well show you a couple more things. Click the Labels button. In the variable label section you can type in a label for the variable you re working with. This is a substitute name for the variable that is used whenever this variable is referred to in the output window. The name for this variable is id, but you might type in subject identification number as the variable label. This is a name that makes it much more clear what kind of information the variable contains. Specifying Value Labels Within the Define Variable window, you can also take advantage of the Value Labels section of the window. Basically, what s going on here is that usually researchers use numbers to represent or code the information on a particular variable. For example, I might have two age groups in my study. The name for this variable is age. In terms of the numbers that get entered into the dataset I ll put in a 1 if they re in the younger adult group and a 2 if they re in the older adult group. So the numbers that appear in the column for the variable age will be 1 s or 2 s which is fine, as long as I remember that 1=younger adult and 2=older adult. But what if I don t use this data file for five years and I forget what the coding scheme is. And, besides, it s just a pain to have to remember this kind of stuff. It would just be a lot easier if we could get SPSS to just say Younger adult and Older adult in the SPSS output when it s referring to the two groups, instead of the just displaying the values 1 or 2. This is where the value labels come in. If I wanted SPSS to say Younger Adult whenever I ve entered a 1 for age, all I have to do is to enter 1 as the Value within the define variable window and then put in Younger Adult as the Value Label. Then when I click Add I see 1.00=Younger Adult appear in the box just to the right of Add. Now I can go back and put a 2 in the Value box, Older Adult in the Value Label box, and then click Add again. Now I ve got value labels for both of the options for that particular variable. If you had a variable with seven different possible responses, you d have to go through the Value, Value Label, and Add sequence seven different times. Okay, now that we ve got some of that stuff out of the way, go ahead and enter the rest of the data. Keep going at it until all of the data are entered. The second variable represents IQ, the third variables represents GPA, and the fourth variable represents

7 7 the subjects year in college. For the variable Year a 1 means that they re in their first year of college, a 2 means that they re in their second years of college, etc. For the variable Year please put in a variable label of Number of years in college. In addition, please add value labels for years 1-4. Use the Descriptives option to get the means and standard deviations for both IQ and GPA and add this information to the Output Window. Save the output window to a file named assign1. Saving a new data file To save the new data file, click file, then save as. Save the file to the a: drive. Now type in the name for your data file. You might name it iq-gpa. SPSS will automatically save it with.sav as the file extension (i.e., the name of the file will end up being iq-gpa.sav). Check your disk to make sure that it got saved. What I d like you to hand in is your floppy diskette that contains your data files and output window file. Remember the fifteen minute rule. Please let me know if something in the assignment doesn t seem to work or if something in the text doesn t look right to you.