Crémieux Profile picture
Jan 8, 2024 • 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.

Shortđź§µ

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 7
Why do identical twins have such similar personalities?

Is it because they're reared together? Is it because people treat them alike due to their visual similarity?

Nope! Neither theory holds water. Image
Despite looking as similar as identical twins and being reared apart, look-alikes are not similar like identical twins are. In fact, they're no more similar than unrelated people.

This makes sense: they're only minimally more genetically similar than regular unrelated people.
The other thing is that twins reared apart and together have similarly similar personalities.

In fact, there might be a negative environmental effect going on, where twins reared together try to distinguish their personalities more!
Read 7 tweets
Dec 2
Society is cognitively stratified:

Smart people tend to earn higher educations and higher incomes, and to work in more prestigious occupations.

This holds for people from excellent family backgrounds (Utopian Sample) and comparing siblings from the same families! Image
This is true, meaningful, and the causal relationship runs strongly from IQ to SES, with little independent influence of SES. Just look at how similar the overall result and the within-family results are!

But also look at fertility in this table: quite the reverse! Image
Source: sciencedirect.com/science/articl…

And to learn more about this general phenomenon, see: cremieux.xyz/p/intelligence… (I've added this citation to this article!)
Read 5 tweets
Nov 25
After this article came out, several people responded, alleging that a cultural model made more sense.

Clark has a point-by-point responseđź§µ

Let's start with the first thing: parent-child and sibling correlations in status measures are identical—hard to explain culturally! Image
The reason this is hard to explain has to do with the fact that kids objectively have more similar environments to one another than to their parents.

In fact, for a cultural theory to recapitulate regression to the mean across generations, these things would need to differ! Image
Another fact that speaks against a cultural explanation is that the length of contact between fathers and sons doesn't matter for how correlated they are in status.

We can see this by leveraging the ages parents die at relative to said sons. Image
Read 10 tweets
Nov 24
The idea:

The internet gives everyone access to unlimited information, learning tools, and the new digital economy, so One Laptop Per Child should have major benefits.

The reality:

Another study just failed to find effects on academic performance. Image
This is one of those findings that's so much more damning than it at first appears.

The reason being, laptop access genuinely provides people with more information than was available to any kid at any previous generation in history.

If access was the issue, this resolves it. Image
And yet, nothing happens

This implementation of the program was more limited than other ones that we've already seen evaluations for though. The laptops were not Windows-based and didn't have internet, so no games, but non-infinite info too

Still huge access improvement though
Read 4 tweets
Nov 22
What is the effect of having a parent get locked away on a kids' own risk of eventually committing crime?

As it turns out, basically nil.

Having a mother or a father locked away doesn't significantly increase risk, and indeed, may reduce it if it happens at an early age. Image
This is relative to no incarceration, so the result should be interpreted as... pretty shocking!

Similarly, we can look at the effects of longer versus shorter parental sentences.

There's seemingly little effect of the length of time parents are incarcerated for. Image
Compare those within-family estimates from above with these between-family results from the same study, period, cohort, etc.

Notice: the apparent 'effects' between families are significant stratified in the same way.

That's an important distinction! Image
Read 5 tweets
Nov 20
Why?

I doubt the answer is weight loss. Consider 2 other drugs for diabetes: DPP-4 and SGLT-2 inhibitors

GLP-1RAs are associated with less Alzheimer's vs. DPP-4is:

But not SGLT-2is:

Neither generates much weight loss, but SGLT-2is match GLP-1RAs on glycemic benefitsImage
Image
So, at least in this propensity score- or age-matched data, there's no reason to chalk the benefit up to the weight loss effects.

This is a hint though, not definitive. Another hint is that benefits were observed in short trials, meaning likely before significant weight loss.
We can be doubly certain about that last hint because diabetics tend to lose less weight than non-diabetics, and all of the observed benefit has so far been observed in diabetic cohorts, not non-diabetic ones (though those directionally show benefits).

Anyway, trials needed!
Read 4 tweets

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