SPSS Data Management Tutorial

Transcription

1 SPSS Data Management Tutorial Social Science Research Lab American University, Washington, D.C. Web. Tel. x Learning Objectives In this tutorial you will learn how to Compute new Variables using the Compute Variable tool. Use the Recode into Different Variable tool to create a dummy variable. How to look only at specific parts of your data and select cases How to merge two data files together to add variables or cases to your dataset. Use SPSS to export data to other programs. For this Tutorial we will be using the World95.sav file. It is available on our website. Transforming Variables There are two basic ways to transform variables compute and recode. Compute allows you to arithmetically combine or alter variables and place the resulting value under a new variable name. Recode allows you to create discrete variables (nominal or ordinal) from either continuous or other discrete variables. Compute Variable Let s create a variable for average overall life expectancy. 1. Go to Transform > Compute Variable. 2. Enter life_expect for the target variable. Then, enter the formula lifeexpf *.5 + lifeexpm*.5 in the numeric expression box. 3. Click OK. 1

2 The Compute Variable interface gives you the option to create new variables. Recoding a Variable Recode: Let s create a discrete, nominal variable for high and low income countries using GDP per capita. Go to Transform > Recode into Different Variables. 1. Select GDP per capita for the Numeric variable box. 2. Click Old and New Values. Select range: LOWEST through box. 3. Enter In the new values, enter Click add. 5. Select range: value through HIGHEST box. Enter In the new values, enter Click add. Click Continue. 7. In output variable, give the name as highlow and the label as country is a high or low income country. 8. Click change. 9. Click OK. 2

3 Your result is called a dummy variable. Dummy variables are useful for seperating your data into useful catagories. For more information on this read the Split file and Select Cases sections Tip: Be careful to select Recode into Different Variables and not Recode into Same Variables. The latter one replaces all of the data in your original variable. Tip: This can also be done to recode interval/ratio/scale variables into Ordinal varibles by creating a set number of discrete categories. Splitting files The Split File option allows you to compare subgroups or organize output by subgroups. Let s organize output by subgroups. Data > Split file > Compare groups. 3

4 1. Select the button by Organize output by groups. 2. Highlight a variable you want, for example, country has per capita income less than or any categorical variable. Click OK. 3. Then do some analysis (for example, run a correlation between literacy and aids rate). The output will show you the results of each group side by side. Tip: You can use Dummy Variables to create groups to compare. Selecting cases The Select cases option allows you to analyze only one of the subgroups of your interest. - Data > Select cases. Check if conditions is satisfied. Click on the if button. 1. Highlight a variable you want, for example, country has per capita income less than or any categorical variable, and put it in the expression box by clicking the arrow. Then specify a subgroup by writing an expression you want. Ex) lowinc=1 2. Then do some analysis (for example, run a correlation between literacy and aids rate. The output will show only the results of the selected group. 4

5 Tip: This tool can be used to remove cases from your dataset, but Selecting Delete unselected cases in the output section of the Select Cases window. If you decide to do this, make sure to Save As your file in case you need to go back to the old version. To turn off the selection, go to Data > Select cases. Check All cases. Click OK. Match merging data files You can merge data from two files in two different ways. You can: Merge the active dataset with another open dataset or SPSS Statistics data file containing the same variables but different cases. Merge the active dataset with another open dataset or SPSS Statistics data file containing the same cases but different variables. To Merge Files go to Data>Merge Files > Select Add Cases or Add Variables Tip: Cases are the data inside of variables Add Cases merges the active dataset with a second dataset or external SPSS Statistics data file that contains the same variables (columns) but different cases (rows). Add Variables merges the active dataset with another open dataset or external SPSS Statistics data file that contains the same cases (rows) but different variables (columns). For example, you might want to merge a data file that contains pre-test results with one that contains post-test results. 5

6 Note: Cases must be sorted in the same order in both datasets. To Sort Cases go to Data> Sort Cases>Select one or more sorting variables. You can also sort cases by right clicking on a variable in the Data view and selecting Sort Ascending The data file is sorted based on the values of the sorting variables. If you select multiple sorting variables, cases are sorted by values of each variable within categories of the prior variable on the Sort list. If one or more key variables are used to match cases, the two datasets must be sorted by ascending order of the key variable(s). Variable names in the second data file that duplicate variable names in the active dataset are excluded by default because Add Variables assumes that these variables contain duplicate information. Using SPSS to export and convert Data Since SPSS can read excel files it is a useful tool for converting excel data into Stata format. SPSS can export files into Stata format by going to File>Save As> In the Save Data As window click on Save As Type to choose the file type you want to convert your data to. 6