As I understand when occurring dummy variable trap ( perfect collinearity ), when you put all category at the same time, SPSS have automatically excluded one dummy as a base line because the summation of all dummy variable in each row equaled 1. we have to put one less category into the regression
By the way, my case I have one question that have 12 categories but each respondents can select 5 out of 12. I have created dummy for each category and put them all, SPSS excluded one dummy. In here I have understood that it caused dummy variable trap because the summation of all dummies in each row equaled 5. As a result, may I confirm that if the summation of all dummy variable are the same number, is that lead to dummy variable trap?
Every comment and suggestion are highly welcome. I will appreciate for your response.
The best way to avoid having all the dummies add up to 1 is to use the most frequently selected choice as your "omitted category." Each dummy variable can then be interpreted as the difference in the mean score for that category versus the omitted category.
Yes, David is correct. You just need K-1 dummy variables, where K is the number of categories.
Thank you so much Sir, for your kind contribution to my question.
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