Consider Reardon, Kalogrides & Shores (2019). They found that even in districts where lower-performing groups had higher SES than Whites, they still tended to perform worse.
In this picture, 79% of the mean Black-White gap is independent of SES. At the metro level, 62% was.
It is a pernicious myth that test scores and achievement gaps are mere reflections of geography and that geography plays a major causal role in test scores.
The truth is that their association primarily reflects selection.
It has to do with Justice Jackson's comments that when Black newborns are delivered by Black doctors, they're much more likely to survive, justifying racially discriminatory admissions.
We now know the study contained fraud🧵
The original article claimed that, when Black babies are attended to by Black physicians, their infant mortality rates decline substantially relative to when they have a White physician.
Justice Jackson cited this in the Supreme Court, even though it was implausible.
A few months back, we learned that the original finding was driven by the authors failing to include a required control variable.
Not only that, but they seemingly knew they this variable was important.
Prior to the fall of the Iron Curtain, markets in Eastern Europe were remarkably inefficient.
After its fall, market reforms occurred, and after they took place, they went from less efficient firms capturing larger market shares to the opposite: more efficient firms dominated!
The thesis is this:
America's stock markets are set up in a way that, incidentally, promotes more efficient firms capturing larger market shares.
There's not yet enough data to know if this is true, but time will tell if this possibility holds up.