I do not know of any published resource that show the percentage of students at a particular school getting their first choice residency. During the match process, the information that the school gets from CASPR is whether or not the students matched and what programs that they are matched to if the student had matched. It does not indicate whether the program was the student is the first choice or not. Of course, it is possible that the school may do their own survey by asking their own students.
In regards to selection criterias for three year residency, gustydoc did touch on a few factors. Many programs have GPA minimums. Hence, your school grades are rather important. CV is important since it reveals your extra curricular activites, research, etc.... Some programs like that students are involved in research. As for what school you attend, it may or may not play a role in getting a three year residency program. If you are applying for a residency program that traditionally take students from a certain school, then attending that particular school would increase your chances of getting into the program. However, most of the top residency programs in the country have taken students from all schools. In general, most of top 10 students from any school would usually get into a decent three year residency program. Gustydoc also mentioned about the externship performance and visitation of residency programs that a student did not get to extern at. As gustydoc pointed out, externships are month long interviews. Visitation of residency programs also show your interest in the residency program. The performance on residency interview is also important. You will be surprise to see that some of the favorite students (based on their externship performance) do not get into a residency program due to their poor performance during the residency interviews.
