[Obi_Juan_Kenobi]

0.5% getting 'professor' positions is just nonsense. Just click the link so see some useful discussion, but it's ridiculous at its face: the average professor is not graduating 200 PhD students. The figure is probably closer to 20 for most fields, which gives a more reasonable 5%. Then you have to consider that many programs offer tenured research positions, but don't take on doctoral students.

Finally, consider that, upon entering a doctoral program, many students don't intend on academia at all. That number drops by the time they complete their dissertations, too.

Ultimately, I'd give a rough figure of 1 in 4 qualified and motivated PhDs getting a suitable tenure-track position in a reasonable timeframe (~4-5 years). Maybe one in five or six will get tenure, in the end. Which is still terrible when you think about it, but the odds aren't nearly as ridiculous as some would claim.

[patall]

Might not be in physics or mathematics but in Life Science it certainly almost is. At the institute I am working right now has about 20 PhD students per full professor (every 3 years anew, so a Professor has 10 times that number in 30 years). Its all a question of associates and other types of group leaders and obviously delegation.

[awiedmer]

That's assuming that tenured positions are not on the decline (they are), and that the number of PhD graduates has not been increasing (it is), and that the funding available to maintain a lab has not gone down (it has).