My curiousity provoked by this question and Igor's answer, I'd like to know: how many mathematics PhD's who want to get a tenured job as a research mathematician actually get that job?

As a first approximation, I'd like to know how what percentage of math PhD's who get a research-oriented postdoc wind up as tenured professors in research-oriented jobs (pick a number of years $n \geq 6$, and determine the percentage of math PhD's who went on to research postdocs that had tenured jobs within $n$ years; the more data, the better).

(Of course I'd be happy with data for any particular region---e.g. US or Europe or Japan or Australia, and it'd be great to have it all; but maybe the US is the project to start with)