MIT and Stanford both use race as a significant factor in making admission decisions. They have explicitly stated this [1]. Caltech much less so (I believe it can be used as a tie breaker). Hence, Caltech is a better control than Stanford or MIT to compare against when you are trying to see what things should look like if race were not a factor.

It's not a perfect control, though, because of Caltech's focus on STEM. Caltech does actually offer non-STEM courses (and majors). In fact, it requires students to take about 1/4 of their coursework in humanities and social sciences, which is similar to what a science major at a good liberal arts school would take. Nevertheless, no one chooses Caltech for the humanities or social sciences, whereas people DO choose Harvard for them.

Although undergraduates are generally not admitted on a department by department basis, surely the schools have to try to get some idea from the application what fields the student is interested in majoring in, and they have to take that into account in making their decisions. If you have facilities for 50 new chemistry majors a year and 50 new English Literature majors a yer, and you get 500 applicants from people whose application suggests they might go into chemistry and only 60 applicants who appear likely to go into English Lit, you are going to reject a lot of those potential chemistry majors, even if their applications look better (grades, tests, and so on) than those of many of the people you accept from the group that looks interested in English Lit.

Since many high achieving Asians are driven by pressure from their parents, and parents push their kids toward STEM a lot more often than they push toward English Literature, it is possible that Asians could be getting effectively discriminated against as a side effect of them concentrating in STEM.

[1] http://findlawimages.com/efile/supreme/briefs/02-241/02-241....