<p>My interviewer for Harvard was a 26 year-old, recent graduate. When I met him in person- all prior communication was through email- I referred to him as Mr. (last name). Immediately he laughed and told me to call him Rich. </p>
<p>My Yale interviewer graduated in the early 90's and was probably 50+. I called him Mr. (last name), the entire time and he seemed to prefer that. </p>
<p>I think that the best thing to do is to refer to them by their last name, and they will let you know if it is ok to call them by their first name. I think age does seem to be a factor, but there are of course many exceptions. I would say people under 35 would actually feel more comfortable if you refer to them by their first name, but there are also exceptions to this too.</p>
<p>I always ask my interviewer what I should call them. Sometimes, they say "just call me such-and-such". I'm on a first-name basis with both my Princeton and Harvard interviewers because of that. Both of them had doctorates so that solved the Mrs./Ms./Miss problem.</p>
<p>I didn't do either. Their names never came up when I was talking to them because I would address them by looking at them. Occasionally, I might say, "sir" but that was rare.</p>
<p>In general you can't go wrong by using Mr./Ms. and waiting for them to suggest using a first name instead. It tends to be generational. You may not need to call them anything.</p>
<p>Yea, but then how to you address correspondence for thank-you note? My d erred on the side of caution, regardless of age and started her notes with:</p>
<p>^^ I would say that is certainly the best way to start thank you notes, unless a google search of the interviewer reveals that he/she holds a PhD, in which case Dr. might be more appropriate, though I am not positive on this</p>