Creating dummy variables involves converting nominal or categorical data into two levels to permit group comparisons between a level of interest and the other levels of the variable. A nominal variable may already have two levels, but its current format may not facilitate statistical analyses. The convention for dummy coding entails assigning a value of "1" to the condition of interest and "0" for the other conditions. You can easily create dummy variables using SPSS statistical software.
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Set up the coding scheme for the variable you want to dummy code. Assign the condition of interest a value of "1" and the value of "0" to the other conditions.
Open your SPSS software and the data file containing the variable you want to transform by dummy coding.
Navigate to "Transform" from the main menu. Scroll down and select "Recode into Different Variables."
Highlight the name of the variable that you want to create a dummy variable. Use the arrow icon or drag to the "Input Variable -> Output Variable:" box.
Select "Old and New Values."
Enter the original value for the condition of interest under "Old Value" and "1" under "New Value." Click "ADD."
Enter the original values for each of the other conditions under "Old Value" and "0" under "New Value." Click "ADD." Repeat the process until "0" has been assigned to all of the other levels of your variable that are not the condition of interest. Select "Continue" when complete.
Input a new name for the dummy variable under "Output Variable." Enter a variable label, a short description of the variable, if desired. Click "Change."
Select "OK." SPSS will transform and code your dummy variable as specified.
Tips and warnings
- Verify the transformations of your dummy variables.
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