Chapter 1: Introduction to SPSS

Transcription

1 Chapter 1: Introduction to SPSS What it is: SPSS is a program that can be used to compute many of the statistical analyses in the social sciences and is commonly used in psychology research and practice. Why it s useful to know: Although you may hope to never see another statistic after this class, you are likely to need a basic knowledge of statistics after graduating with a psychology degree. If you plan to attend graduate programs in psychology or related fields, you ll likely complete a thesis of some sort and it s much easier to use SPSS than hand calculate every analysis. You may also be expected to know stats after graduation. As a therapist, for example, you ll need to be able to identify the best treatments for your patients (based on research articles with, yup, stats!). If you don t plan to attend graduate school, you ll still be expected to be able to understand or even conduct basic statistics (some psychology students are even hired for this ability!). If you go into an area like business or human resources, you ll often be asked to identify whether a particular program is working and that based on, you guessed it, stats and SPSS or some similar program. Opening SPSS 1. Click the Start button in the bottom left hand corner of your computer screen and a pop up menu will appear. 2. Highlight programs or all programs. This will open another pop up menu on the side. 3. Highlight SPSS for Windows or SPSS Inc. Another pop up menu will appear. 4. Choose SPSS (you do not want the authorization wizard, just the program. 5. SPSS will open and a pop up menu will appear asking what you want to do. Just cancel out of the menu. 6. You re ready to open or enter data! Opening Data Files We ll talk about entering data from scratch in a few minutes, but first let s open a dataset and get familiar with SPSS. 1. Click on File in the upper left hand corner of SPSS, highlight open, and click on data. It will look like the screen shot below.

2 2. This will open a browser window, just like the one you see any time you are looking for a file on your computer. Locate the data file called ch 1 example.sav by browsing through the computer files you ll notice that only SPSS data files are visible. Your TA will instruct you where to find the file for this example. 3. SPSS will open the dataset. It should look something like this: ***Note If your screen does not look like the screenshot above, you may be in Variable View instead of Data View. To switch from Variable View to Data View, simply click on the

3 Data View tab in the bottom left hand corner of the screen. Once you are in Data View, your screen should look the same as the screenshot above.*** Exploring SPSS Now that we have a data file open, let s explore SPSS. The first thing to notice is that there are two tabs in the lower left-hand corner labeled data view and variable view. You can use these tabs to navigate between your actual data and information about what the data represent. In the data view, you ll see that there are 3 columns participant, year, and age. You ll also notice that there are rows and that each row contains a number in each column. Each row represents a different case (a different person in our example) and associated data. In our example data set, each row is a different person and their scores for year and age are on that same row. For example, in row 1, you ll see that participant #1 has a score of 1 for year and a score of 18 for age. Alas, you don t know what year or age means. But wait! If you hit the tab labeled Variable View in the bottom left-hand corner, your view in SPSS will change. It now should look something like this: Each of the columns from the data view window are now displayed on separate rows. You ll see that participant is now on row 1, year on row 2, and age on row 3. There is lots of useful information contained in variable view that will help you figure out what the data displayed in data view means. Let s look at the participant row first. 1. The Name column tells you the variable name that will appear at the top of the column in the data view.

4 2. The Type column tells you that the data contained in that variable should be numeric (i.e., a number). In other words, you can t just write One you need to enter the number 1. Every variable we deal with during this semester will be numeric. 3. The Width column tells you that you can enter eight numbers. If you had numeric data that went to the billions, you would need to adjust this so that your data will fit in the column. 4. The Decimals column tells you that the variable will be displayed to two decimal places. This is pretty standard, but you can adjust it if needed. 5. The Label column is very important. It gives you a longer description of the data contained in that variable. You ll see that for participant the label tells you that the variable represents participant number ; for year the label tells you that the variable represents year in school; for age the label indicates it is participant age. So now you know what data was collected in this study a number of participants year in school and age were assessed. 6. The Values column is also important. Any time that you have a categorical variable (i.e., nominal or ordinal data that represent discrete categories, such as gender or year in school), numbers are assigned to represent each level of the category and sometimes these are arbitrary. For example, if you collected data on gender you might give any man a score of 1 and any woman a score of 2, but no one except you would be able to tell what the numbers meant (and you might forget what your own codes mean if you don t use the data for awhile!). The values column lets you communicate what numbers have been assigned to which categories. If you have a continuous variable (like age), you don t need to identify the value labels because they are not arbitrary scores (a score of 18 on age means that the person was 18 years old). Right now, you can t see very much of the information. Click in the Values column for year and a small gray box will appear. Click on that box and a pop up window will appear. It should look like this: You ll see that a score of 1 means the person was a freshman; a score of 2 means the person was a sophomore; and a score of 3 means the person was a junior. You ll also see boxes to put in more values, but we ll come back to that in a few minutes.

5 7. We won t change values in the remaining columns this semester, but they can modify the appearance of the data and keep track of missing scores in the data set. If you switch back to data view by clicking the tab in the lower left-hand corner, you now have enough information to understand the data. Participant number 1, for example, is an 18-year old freshman. If you scroll down through the numbers, you ll see that there were 90 participants in this study. Go ahead and close this file (don t save!) and reopen SPSS we ll look at how to create a data file from scratch. Creating a Data File Imagine that you are a researcher interested in student s school spirit at universities of different sizes. You ask 10 students at different large public and small liberal arts colleges to rate their school spirit on a scale from 1-7, where 1 means no school spirit and 7 means intensely school spirited. Here s what that data looks like in raw form: School Size School Spirit Score Small 1 Small 1 Large 7 Small 2 Large 6 Large 5 Large 7 Small 3 Large 6 Small 3 We ll talk in later chapters about how to conduct analyses to find out if there s a difference in school spirit between small and large universities. Before you can find out, all the data needs to be put in SPSS. 1. Open SPSS using the instructions above. 2. The first thing you need to do is set up your columns for each variable. Switch to Variable View using the tab in the lower left-hand corner. It will look something like this:

6 3. Your first variable is always participant number. This helps you keep track of which participant is which this is handy when you have surveys from hundreds of people and need to double check something! In the Name column type in Participant and hit tab. You ll see that SPSS automatically fills in the rest of the information to the most typical default values. It should look something like this: Go ahead and fill in the label with a longer description. This can be whatever you want but should concisely describe what the variable represents. For this one, you can put Participant Number as the label. Now follow the same procedure to set up the variables for school size and school spirit. The database should look something like the one below:

7 It would probably be useful to include labels for these variables so it s clear what number corresponds to different size schools and what the ratings of school spirit mean. To include a label for the size variable, click in the cell in the values column on the size row. A gray box will appear. Click on the gray box and a pop-up window will open like this one: Now you ll tell the program what number corresponds to each size of university. We ll assign a 1 as small and 2 as large, but these are arbitrary and you can create whatever values you like. To add them, put the number 1 in the box Value:. Then put small college in the box Label. It should look like this:

8 Hit Add and you ll see the value appear in the white box. Then repeat the process by putting 2 as the value and large college as the label and hitting Add. The box should look like this: After both values appear in the white box, click OK. Repeat this process for the school spirit variable by setting 1 to mean no school spirit and 7 to mean intensely school spirited (you don t need to define all possible values, you can just say what 1 and 7 mean this way you remember what you asked even years later). 4. Before going further, you want to save your work. To do this, click on File in the upper lefthand corner and choose save as. Browse through the window to determine where you d like to save the file. Type in a name for the file and then hit the save button. When using SPSS, it s helpful to save your work often. 5. Now it s time to enter your data. Switch back to data view. You have ten participants, so you can put in numbers 1 through 10 as the participant numbers. Then, consulting the table of data above and remembering the values you assigned to the school size, go ahead and fill in the information for each participant. When you finish, it should look something like this:

9 6. You always want to double check your data entry because just one mistake can cause you to reach the wrong conclusions about what happened in your study. Consult the data table and the SPSS file again and just double check that everything matches between the two. 7. Hit the diskette icon on the tool bar to save the updated data file. Congratulations! You have conquered the first and most important step with SPSS getting data into the data base! We ll use SPSS in the following chapters to ask interesting questions about our data, but in case you re dying to know, yes, school spirit significantly differed between students at small liberal arts and large public universities. In this example, participants from large public universities reported that they had more school spirit than participants from small liberal arts universities. Maybe Aggies were in the sample!

10 Practice Problem #1 for SPSS (answers in Appendix). Imagine that you are hired by a local gym to evaluate customer satisfaction with several exercise programs they ve recently made available. You collect data from 15 people who have taken part in both exercise programs at least once. You ask the following questions: 1. You recently took part in the new spinning class and the water aerobics class. Take a moment to think back to these experiences. Which class did you enjoy the most? 2. For the class that you enjoyed the most, how important was the social aspect of the class to your enjoyment? Not at all important Very important 3. For the class that you enjoyed the most, how important was the rigorousness of the exercise to your enjoyment? Not at all Very important important You collect the following responses: Class Enjoyed Most Importance of Social Importance of Exercise Aspects Spinning 6 7 Spinning 5 6 Spinning 4 7 Aerobics 5 1 Spinning 6 5 Spinning 3 4 Aerobics 1 3 Spinning 5 6 Aerobics 6 6 Aerobics 2 5 Aerobics 5 4 Spinning 2 3 Spinning 7 2 Aerobics 5 7 Aerobics 5 1 Create a database with all of the relevant variables, including labels, and enter the data. Don t forget to save!