While it appears to be standard practice in all the examples I've heard of for examining committees to conduct their deliberation in camera, I've noticed that the rules regarding who can attend what parts of a PhD defense vary significantly around the world and even between institutions within the same country.
What are the justifications/arguments for greater/lesser restrictions on who can attend which parts of the defense?
There doesn't seem to be a question about this on SE already, though I've seen some answers on other forums. The answers to this related but not applicable question do provide some insight. I found a blog post that seems to indicate that in the US the method by which defenses are conducted is a legal matter.
At my institution (Canadian, public university) the list of people who can attend what we call the Final Oral Examination, or colloquially the PhD Defense, is highly restricted. There are multiple steps to completing the PhD degree requirements here:
- A Department Defense, where the PhD candidate gives an open seminar at their department. The examination committee does not need to attend this one. Usually it is just attended by your supervisors and some fellow grad students. Supervisory committees can, and often do, vote to skip this one entirely.
- A Final Oral Examination, which is conducted entirely behind closed doors. The examination has three parts: the presentation period (20 minutes), the question period (60-120 minutes), and the deliberation period (10-30 minutes). The candidate leaves the room during the deliberation period, and then returns for the committee to give their decision (pass/fail).
The only people, other than the candidate, allowed to attend any part the Final Oral Examination are the members of the examining committee, a chairperson appointed by the faculty, and any member of the faculty at the university (upon the invitation of the chairperson). The one exception are "qualified observers" which must be approved in advance by writing a letter (in hard copy) to the Vice Dean of Graduate Studies. The deliberation period is attended only by the committee and the chair.
My understanding is that this is highly restricted compared to other institutions, even within Canada. On the other hand, when I defended my Master's degree at another Canadian institution, I invited my best friend to attend (he wasn't even a student at the university). These other attendees were allowed to be present for everything except for the deliberation period. My understanding is that this is very open compared to other institutions.