[lizzy]

Depending on the school grad students are not necessarily cheaper to a professor than Postdocs due to the overhead/fees paid for students versus that paid for postdocs. Also the current academic job market in the US is bad. Taking a postdoc for 1,2,3 years has been very common in Computer Science for people seeking faculty positions in the last couple of years.

[drbaskin]

The same is true in math -- it is rare for mathematicians to move directly from a Ph.D. to a tenure-track faculty position.

[lizzy]

Agreed. In fact I wonder what discipline it is not true in at the moment.

[drbaskin]

I've heard that it's possible (not easy) for statistics Ph.D.s to jump directly to faculty positions, but I think this is becoming less common. I think that economics Ph.D.s also often jump directly to faculty positions.