I too respectfully disagree with TherapistForChnge regarding a LOR from an MD -- if by MD we mean a psychiatrist. By no means would a letter from a psychiatrist be discounted by a clinical program. Such a statement by TFC also implies that it would be bad judgment for an applicant to submit such a LOR. Frankly, this is just not true. It is extremely common for applicants to clinical programs to have a background as a research assistant (paid or unpaid) on studies whose PI is a psychiatrist. Though yes, as TFC noted, the model of MD training different than that of a psychologist, a good psychiatrist MD is psychologically-minded. Therefore, they can provide solid judgment in the LOR as to whether you too are psychologically minded, and to what degree. Also, if you are doing research for the PI and you are applying to PhD programs, you most definitely would benefit with a LOR from the psychiatrist to speak to your research accomplishments, and clinical skills if your research involved clinical aspects. Even if you plan on psyD programs that are really only clinical in nature, and your RA position involves no clinical aspects, the LOR from the psychiatrist PI can speak to your professionalism, social skills dealing with your colleagues and advisers, and attest to your hard work. And perhaps the clinical qualities you bring to your research experiences. These are important applicant characteristics that admissions committees seek. But, as TFC also importantly noted, different programs have specific requirements regarding who they want your letters written by. Some programs may require that all 3 LOR be written by professors of your classes. So, as is the case in any endeavor, read the admissions requirements carefully, and plan accordingly. It may be preferred to have clinical psychologists rather than an IO psychologist write your LOR. But again, if you have a close relationship with that IO psych, and they know how to craft an appropriate letter, and without that letter you're short of a LOR, don't freak out. I happen to have done research in the past with a PI psychiatrist. However, almost all the RAs there planned to apply to clinical doctoral programs, not psychiatry. The psychiatrist PI wrote a LOR for those determined worthy of a LOR. They now attend extremely competitive clinical programs. From your posting it appears you have sufficient time to place yourself in the best situations to get the most useful LOR. And take MarkP's advise to task too in terms of going out of your way to develop close relations with your professors. Glowing LOR with a poverty of specifics to back up what's written are the types of letters that, while not discounted, will not weight as heavily as those letters that speak to specifics. Good luck.
