First I have to make it clear that I understand the SOP is not just written for my potential advisor to view; it will certainly be presented to the admission committee first. However, my potential advisor will be the only person who reads both of my SOPs. Below is the complete question with background information:
I am currently applying for psychometrics in both Department of Educational Psychology and Psychology (Quantitative psychology) in the same university. My potential advisor is a faculty member in both departments, doing research on XXX. When I wrote my SOP for psychometrics in Educational Psychology, I only talked about my research interests in XXX.
Now I am adapting my SOP to application for Quantitative Psychology which allows students to do research in collaboration with other fields in psychology in addition to their own research interests. I am interested in doing research in the Social Psychology and am considering if I should include this in my SOP, given I only mentioned that I am interested in XXX in my SOP to Educational Psychology? In addition, XXX is really different from social psychology in general..in other words, my two research interests are not relevant.
As my potential advisor will be reading both SOPs, I am afraid that having talked about additional research interests in my application for Quantitative psychology would make me appear not firm about my research interests in XXX (am I overthinking about this?) Or is it even necessary for me to mention my research interests in social psych in my SOP, as I will be given opportunities to work on research in other fields of psychology, including social psych, anyways?
Additional information: my potential advisor knows that I am interested in social psychology as I mentioned this to him. Nonetheless, we never had a talk about my research interests in social psych.
In short, 1) do I need to talk about my research interests in social psych in the SOP to Quantitative psychology? 2) if I do, what's the best approach to avoid my advisor feeling confused about my research interests? (for example, just vaguely mention that I would be excited about doing research in social psych etc. ?)