Getting into a PhD program is one thing, completing it is another. Here is an interesting report
by University of Maryland, published in June 2006.
The report gives broad stats on the likelihood of completing the PhD based on different characteristics of the PhD students.
It then suggests to the University
how the grad school can improve the completion rate, e.g. thru 1) effective mentoring, 2) financial support, 3) grad student support, 4) programs, departments & colleges, and 5) grad school's role.
Although the purpose of the report is to help the University to increase the proportion of PhD students who complete the program, grad students applicants can make use of the suggestions listed in the report in choosing a school where they are likely to complete their PhD pursue. E.g. we choose a school that have sufficient financial and grad students support. Of course, some things can only be discovered after we getting into the program (e.g. effective mentoring). But overall, I think this paper is worth the read.