Title. What role do they have? Who has the final say after the interviews? I would imagine it differs program by program, but what does the general process look like?
In our program, two trainees in their graduate phase are fully fledged voting members of the committee. Their interview scores count as much as mine. That is not the average MSTP but gives you an idea...
Very different between schools. Roles range from interviewing applicants (these interviews really do count) to screening applications and voting on the admissions committee.