Interview visits: How to answer the question "What other universities are you considering/interviewing at?"

[Biostudent]

I have applied to PhD programs in biomedical science, and so far I have attended two interview weekends. One question that continues to be brought up in these visits by professors is "What other universities are you considering/interviewing at?" 

I was wondering if someone familiar with the PhD interview process could tell me two things:

1. Why do professors/interviewers ask this question (do they want to know what schools are they competing against for students, or are they evaluating me in some way?)

2. What is the best way to answer this question? (I have just been answering by telling them the schools I am interviewing with, but honestly is it really their business to ask or know where else I am interviewing at?)

Thanks for any advice.

[fuzzylogician]

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