My continued assertion is that "hard data" can be misleading, wrong, and discriminatory. It requires judgement to understand what it tells us and whether there is error in the collection of the data itself.
As far as Kaplan, I don't have metrics to share, but what I saw shocked me at the time. It appeared as though they collected data as to how much their test prep improved scores and it was pretty dramatic. And, they were smart enough to distinguish between their test prep books and their in person tutoring. In person tutoring worked better and by a lot, but it all helped.
As far as tests, I've never contended that they shouldn't be done, but that these scores need to be part of an overall portfolio. I have in fact sat on admittance boards for graduate school and the two dominant factors other reviewers used were GPA and where they went to undergrad. Both of these were hard metrics and full of bias. I'll also contend that they weren't particularly effective in identifying students who successfully completed the program.
Something to consider, I do think test scores can help screen candidates. For example, if one is going to admit into a math program, then their quantitative score should probably be above a certain level. After that, I personally don't think it matters. In that way, one could just set minimum criteria to be accepted, which includes GPA, tests scores, research, jobs, whatever, and then randomly select from that group. That would certainly eliminate a huge amount bias, though not all, but most people hate this approach because it contradicts this belief that we live mostly in a meritocracy. They want rankings and they want to know who number 1 is. My continued argument is that it's impossible to distill a person down to a hard ranking in a reasonable matter, especially with test scores, and it's not necessary for college admission since one can select a group of applicants for acceptance without ordering them.
I appreciate your willingness to engage and your detailed responses. I understand where you're coming from, and that you've seen how the sausage is made.
> In person tutoring worked better and by a lot, but it all helped.
Are money and other resources only helpful for getting a good test score? They don't matter at all for the factors that improve one's chances of admission? For example, going to a good high school district, participation in certain sports, hobbies, or access to internship, volunteer, or research opportunities?
My argument is simply: by making it about the test, you remove all the other factors where money could potentially have an influence. The rich students will get tutoring no matter what. But they can't gain any other advantages over the poor students.
> In that way, one could just set minimum criteria to be accepted, which includes GPA, tests scores, research, jobs, whatever, and then randomly select from that group.
That wouldn't be a terrible approach either. You are correct it would be unsatisfying.
> GPA and where they went to undergrad...were [both] hard metrics and full of bias.
I would argue they weren't "hard" at all. Undergrad is already gated by "squishy" criteria. Normalizing GPAs across universities (and countries, in the case of international applicants) is tricky and imprecise.