Crémieux Profile picture
Jan 8 • 10 tweets • 3 min read • Read on X
Achievement gaps do not simply reflect geographic sorting.

This fact has been known for more than a century now, but some people still don't get it.

Short🧵

First: achievement gaps exist within the same schools.Image
This is not just true for race, it is also true for class. Image
When it comes to district-level family incomes by group, we see that intercepts differ.

In other words, even when lower-performing groups are wealthier, they tend to do worse than higher-performing groups. Image
If you're reading this, you probably know that this replicates the results for rearing household income (1/3):
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. Image
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.
I neglected to mention this: results from Moving to Opportunity suggest no significant effects on test scores.

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More from @cremieuxrecueil

Dec 18
College students make or are forced to make suboptimal choices about the times their classes take place🧵

For students who register for 8AM classes, about a third wake up after class starts, and almost 40% wake up too late to get to class on time. Image
People's internal rhythms aren't things they just choose, they're somewhat out of their control because they're synced up with day-night cycles.

Consider this, showing the amount of time 8AM class-takers sleep on school days vs weekends (gray), measured through logins at school. Image
If you compare those 8AM class-takers to 9AM students, you see that the ones who registered for 9AM classes sleep longer, but both sleep similar lengths on weekends. Image
Read 16 tweets
Dec 16
If you're curious about the recent rise in autism diagnoses, go read this.

It details how much of the rise in diagnoses is down to diagnostic drift and increasing screening. Image
You can see the impact of this on correlations between autism and other things in the published literature:
A common retort is 'But [this] study used the same definition over time and found an increase'. That comment is usually just wrong.

What people see in those studies is almost always a combination of 1. screening more, and 2. screening less stringently even if they don't want to.
Read 5 tweets
Dec 13
The potential gains to port automation are so enormous that Trump is making a huge mistake if he goes along with wishes of the mobsters in the ILA.

The gains on the table are so large that increasing an average port's capacity by just one ship increases total trade by 0.67%. Image
Bulk freight carriers also hate waiting around. They want to take goods and get them delivered where they need to go.

But America's ports are so inefficient that bulk carriers opt to go to the wrong ports to save time.

America's roads get sacrificed to its lack of automation. Image
Want to get automated ports and make America richer?

Destroy the ILA. Don't negotiate with them, just end them outright. The easiest way to do that is to make them happy with being destroyed.

Just Pay Them Off. Image
Read 4 tweets
Dec 12
The COVID era Paycheck Protection Program was defrauded at an incredible scale. People received PPP loans for total nonsense at stunning rates.

Thread of funny claims.

Dodge Hellcat LLCImage
Reparations for Indigenous People LLCImage
Just Traffic TicketsImage
Read 26 tweets
Dec 11
"A reminder: the US has the #1 most expensive healthcare system in the world, yet we rank roughly #42 in life expectancy."

Brian Thompson's murderer wrote that in his manifesto.

Both claims are bad. The first one, because America spends the most on healthcare because it's rich: Image
I don't mean Americans pay higher prices for the same amounts of care, but that Americans consume much higher volumes of care. They do more check-ups, get more screenings, take more tests, dose more drugs, get more surgeries... and so on!

You can predict spending from volumes:Image
Regarding the second claim, Americans have shorter lifespans because they're fat, violent, and reckless, not because of things that the health system can control.

And, if anything, when it comes to the things the health system actually controls, they generally do better!Image
Read 4 tweets
Dec 11
In Medicare Advantage, the government encourages insurers to pursue perverse incentives.

These see them overdiagnosing patients for conditions they often do not have, and which they don't recommend treating, because it means they can send the government a bigger bill. Image
Insurers have tried to claim that they don't do this, and that this data misrepresents the care they provide to patients they diagnose with particular conditions (like HIV!) because COVID disrupted care, but they're lying and it's too obvious. Image
Medicare Advantage does beat FFS on performance and on cost, and it certainly leads to more care for tons of people, but like every major program in medicine, it gets defrauded to the tune of tens of billions of dollars.

Oh well!
Read 4 tweets

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