<p>Here’s the problem about expecting an honest answer from alumni: presumably (and I’m assuming we are talking about doctorate holders), the alumni are now colleagues of the professors the OP is asking about. Unless there is some confidentiality mechanism in place, alumni/colleagues are unlikely to say anything bad, especially in writing.</p>
<p>Talking to graduate students is indeed a whole other story, although even then you might not hear all the dirt. Going to open houses/interview to gain a sense of how the students interact with the professors is an important piece. Unfortunately, you sometimes have to read between the lines. Chatting with graduate students about the general lab/working atmosphere with the PI is fine, but asking them to critique the PI’s performance can be dicey, especially if you do it via email which puts their thoughts in writing. Besides, most graduate students can be assumed to be working with a particular PI for a reason. </p>
<p>Graduate students are generally much more honest with one another than they are with outsiders, but, of course, that depends on both the program and the individuals. As a prospective student, you are more likely to hear the good stuff over the bad, although again, read between the lines. </p>
<p>As I said above, unless you were accepted to work with a specific PI,. you must consider all the researchers in your specialization as possible mentors. If you get your heart set on one because of what graduate students say, then you may be disappointed. Professors often turn down graduate students who want to work with them because of limited resources or other factors. It happens. Of course, all this changes if there is only one possible PI. In that case, your first step is always to make sure that person is accepting students. Next, chat with the graduate students in the lab to get a sense of the dynamics and the research. Look at recent publication history. Although none of this is foolproof, it helps to gain a sense of the program/PI.</p>
<p>I don’t often disagree with Juillet, but in this case I really don’t think you’ll get an honest answer from alumni. And I don’t think you should expect graduate students to say anything bad about their PI. HOWEVER, I do think you should talk to graduate students about their experiences, and you should find out whether your POIs are accepting new students.</p>