This is a fairly wonky post, so be warned.

Some readers have objected (quite reasonably) to the Discriminations post I linked to yesterday — there was a statistic with a very low sample size. To correct for this error, I put together a spreadsheet combining the three datasets referenced in the post. I’ve removed the MCAT/GPA combinations for which no one of any race was admitted, and those for which there weren’t at least 20 applicants of each race.

On the left, I have the raw data: the admissions rates for Asians, whites, and blacks to U.S. medical schools, arranged by their MCATs and GPAs. Just looking at the numbers, it’s clear that preferences can have a big effect.

On the right, I’ve calculated the Asian and black advantages, relative to whites, in the form of the percentage-point differences in the rates. If a score in this category is 10, it means that 10 applicants out of every 100 will get in who wouldn’t have had they been white. Obviously, these numbers are lowest around the edges (if virtually no one of any race, or almost everyone of every race, is admitted, the difference is small).

Asians definitely face an additional burden (most of their numbers are negative), but relative to whites, there’s rarely more than a 10 percentage-point difference. Black admissions are a different story. For “borderline” students — those with MCAT scores between 21 and 32 and GPAs between 2.8 and 3.79, particularly when both scores are in the middles of those ranges, or when one is high and the other low — the black advantage often exceeds 50.

The biggest preferences go to black applicants with MCATs between 24 and 26 and GPAs between 3.2 and 3.39; of every 100, almost 62 get in who wouldn’t have had they been white. By filling in the “black” box instead of the “white” one, an applicant in this category boosts his chances from 15.3 percent to 77.2 percent.

Of course, I haven’t done anything here that the Center for Equal Opportunity hasn’t done better about a bazillion times. But it’s worth remembering these numbers when people say affirmative-action is just a tiebreaker.