Princeton doesn't have any professional schools so no law degrees, medical degrees, or MBA's to fill the ranks with...
Correct. Princeton also has a small student body, it probably outperforms on a graduate per capita basis.
How did you calculate that?
Indeed. Also observable in the fact that while Harvard is the wealthiest school on an absolute basis, Princeton has the largest endowment per enrolled student. Harvard is more than twice the size of Princeton.
Similarly, I was surprised at how few had gone to John Hopkins, which also had a prestigious foreign service/ international relations program.
I have a feeling more SAIS alums end up in policy or foreign service jobs rather than pursuing politics.