http://www.sciencedirect.com/science/article/pii/S1072751505018636
http://www.ncbi.nlm.nih.gov/pubmed/21292930
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2951767/
http://www.ncbi.nlm.nih.gov/pubmed/22911295
Research say's otherwise, your a practitioner of evidence based medicine aren't you? USMLE step 1/2 are the single strongest indicator of a successful resident(not the only), that is why they made it. Note that NONE of these studies cited the school being a significant factor. Ill give you this, an SGU student can bump there score up a bit due to extra time. However by your own argument a DO student or low-tier MD with a high USMLE is superior to a high-tier MD w/ lower usmle since they have less/same time to study for it.
Prior medical school is predictive of three things:
1)You probably were exposed to some rare pathology that smaller schools/community based programs did not see.(This can be overcome by doing away rotations)
2)you did better in your UG education and/or built a stronger resume.(who cares about this after med school?)
3)you had access to better research(does not mean you took part in it).
People from top 20 schools are, in general, very bright individuals. For that very reason they should have higher board scores as well, if they cannot stack up then they have obviously gotten lazy and failed to take advantage of all that their school offers. Why would you want that resident?
In my own experience this seems to be the case. The best residents I have seen while shadowing(UCLA, UCI, UCD, Loma Linda) were not always from high end programs. They did all have high USMLE scores however. Furthermore some of the best researchers in my area went to non-prestigious programs.(the top heme-onc guy is a DO w/ >200 publications)
high usmle tells me 2 things
1)they learn fast
2)they are hard workers
These are the two traits that every resident needs.
Applicants should not be screened by school attended or degree, they should be screened by step 1/2 scores and class rank 1st, then other factors should be accounted for like research experience and yes, even school attended. Doing it any other way makes programs lose out on some great talent and is a slap in the face to hard work.