Early in my (academic) life, I was told that it is appropriate to address a faculty as Professor only when he/she possesses the full Professorial rank and I would be better off addressing Assistant and Associate Professors as Dr.X, especially in written communication. However, recently I have been corrected that it is appropriate to address as Professor, faculty of all three ranks irrespective of them possessing a doctorate. So, my first question is, whether it is okay to address an assistant (or associate) Professor as Prof.X with regard to American universities.
Second, I have been told that these professorial ranks are often a source of ego and resentment. In previous letters, I have unfortunately written something along the lines of "I am interested in the research work of Prof. X and Dr.Y". I wish to know whether addressing them as such, with the obvious distinction would lead to ego issues, or any problems in general.
Perhaps the second question does not belong on this forum. Still, I would appreciate if someone from academia or otherwise could clear them for me.
Best Answer
Perhaps this specific point wasn't terribly clear in my answer to the question Theta30 linked, but to answer your specific questions:
Yes, you may address a professor of any rank (associate/adjunct/assistant) as Prof. X in most universities/depts in the US. In fact, despite not being strictly accurate, faculty who hold lower ranks (instructors, lecturers) are also referred to as Prof. X by students in some institutions.
I can't really give a straightforward answer to your second question as whether it would hurt someone's ego is mostly dependent on the person. I've known some professors who have a preferred title and take offense when anything else is used, and I've known some who are fine being called by their first name by complete strangers. In general if you want to be safe, you might try using the same title if one is applicable to both parties. E.g. if they both hold doctorates, something like "the research of Drs. Smith and Jones" or if they're both faculty members "the research of Profs. Smith and Jones".