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 >= 6 after receiving the PhD; the more data, the better).