I am running a model in which I want to explain my dependent variable with the racial/ethnic diversity in a person's residential area. Diversity is measured with 4 continuous variables. Each one of these variables gives me the percentage of the total population of a racial/ethnic group in the residential area. That means that putting all of them together is the complete population and I should only include 3 of the variables in my model because of multicollinearity.
Now here is my question: How do I interpret the effect of the other variables that I included in the model? Their effects depend on the variable that I left out. Does the model give me the effect when the left out variable is zero or the mean?
I cannot find anything on this online and would be very happy if someone could help me with this question.