So I went ahead and did some quick recalculations by matriculants from each "tier" of undergrad institution rather than pure volume.
Here is what I got:
Percentage of MD/PhD seats filled by undergraduates from the top 10: 22%
...from the top 20: 34%
...from the top 30: 43%
Of the top 30 schools, 4 of them are public and they are [ school (USNWR rank) ]: UC Berkeley (20), UCLA (23), U Michigan - Ann Arbor (29), and UNC Chapel Hill (30).
I also used
@efle 's data from a thread in pre-allo to determine what percentage of the pre-med applicants from a particular institution eventually became MD/PhD matriculants. The fractions were predictably very small.
Take the few schools that supply the most MD/PhD matriculants for example:
School Name (# of MD/PhD matriculants) - Percentage of supplied applicants who become MD / PhD matriculants
1. Harvard (25) - 7.7%
2. UCLA (20) - 2.1%
3. Cornell (19) - 3.7%
3. Yale (19) - 8.2%
5. MIT (18) - 17.8% (nearly 1/5th of MITs applicants go on to become MD/PhD matriculants!! Notably, MIT only had 101 MD or MD / PhD applicants in 2014)
6. UC Berkeley (17) - 2.2%
So one fifth of MD/PhD seats are filled by top 10 applicants and nearly half are filled by applicants from just 30 schools, most of them private. Also, MIT is an extraordinary producer of potential physician scientists.
What is missing is data of class composition by program ranking. My hypothesis is that schools at the tippity top are almost exclusively populated by applicants from top 10 institutions (
maybe top 20) and as you decrease in ranking class diversity actually begins to increase, suggesting that the bias for pedigreed undergraduates is most present at, somewhat predictably, elite dual degree programs themselves.
UPDATE: As an exemplar of my above hypothesis I tabulated Harvard's MSTP class data from the past 7 years and got the following results:
N = 163
% From Top 10 Undergrad: 72%
% From Top 20 Undergrad: 81%
% From Top 30 Undergrad: 86%
A few schools within the Top 10 are very well represented:
% HMS MSTP students from Harvard: 24.5%
% ...from MIT: 11%
% ...from Yale: 9.8%
% ...from Stanford: 7.4%
% ...from Princeton: 4.3%
57% of HMS MSTP students come from just 5 undergrads, typically known among helicopter parents and high school students as HYPSM (or in this particular case, HMYSP) and fully a quarter were Harvard undergrads as well.
URM Info:
% URM: 6.8%
% From Top 10 and URM: 1.2%
(precisely 2 people lol)
% From Top 20 and URM: 1..8%
(3 people)
% From Top 30 and URM: 1.8%
(3 people)
% Of URM coming from Top 10, 20, 30 as a fraction of all URM students: 18%, 27%, 27%
Furthermore, of the HMS MSTP students who did not graduate from a Top 30 undergraduate, 35% were URM. Two thirds of the URM students at HMS' MSTP graduated from non-top 30 undergraduate institutions.
NOTE: Universities without USNWR ranking such as Williams, Amherst, Swarthmore, Oxford / Cambridge etc were assigned the next best available ranking. There were very few of these schools included in the data (Williams is the largest with 4 matriculants across 7 years).