If I'm not mistaken, most PhD students (at least in the sciences, which is the field I'm most interested in) are funded. They're provided with a stipend, and all tuition fees are waived. In other words, it's effectively a low-paying job for them. My question is, why fund PhD students instead of postdocs?
I'm dismissing the altruistic reason ("we fund PhD students as a service to the community") immediately since it doesn't make sense - presumably if someone is spending money in this fashion, they'd fund need-based scholarships. The only other reason I can think of is that the department wants something out of the PhD students - presumably research output; can't think of anything else - that they think they're getting a good deal on.
Now according to Google, the typical PhD stipend is about $20-25k / year. Meanwhile, the typical postdoc is paid $47k / year. That means that a department can hire approximately one postdoc per two PhD students. To that we can add:
- Postdocs have already been trained; PhD students are in training. Postdocs should hit the ground running while PhD students take time to get up to par.
- PhD students especially in 5-year programs spend the first couple of years taking courses, i.e. not doing research work.
- Postdocs can do other things like supervise Masters students that PhD students can't.
- PhD students apparently have a high attrition rate, as high as 50%. Postdocs have been in the business longer, so presumably are also more aware of what they're going into.
It seems more sensible to me that departments should concentrate all funding on postdocs, and leave PhD students to pay for their own education. This is already the case for undergraduate studies. Why do departments continue to fund PhD students?