those born in 1991 scored about five points lower than those born in 1975, and three points lower than those born in 1962.
This is in Norway, and it controls for parental IQ. Pointer from Tyler Cowen.
My question: did Norway adopt the pediatric advice to have infants sleep on their backs, and if so, over what time period was this advice taken up?
Two thoughts: (1) differences in testing more homogenous populations (like Norway) and less homogenous populations–will the study be replicated elsewhere; and (2) if assortive mating is a thing, then is it possible that the lower-end of the spectrum is larger and/or dropping faster than the upper-end of the spectrum?
If this were due merely to pediatric advice for sleeping on your back, I’d be shocked.
Well, for one thing, if people really believed something purely in the environment was causing a continuing trend of an average 5-point drop in IQ in just about 15 years, despite what we might guess to be the maintenance of the modern conditions that led to the Flynn effect in the first place, and perhaps even worse because masking what could have been additional positive increases in the absence of the new negative Bratsberg-effect, it would be cause for justified alarm and panic – the ‘public health and education’ crisis of our time. “Good Lord, please return to the practices of 1975 immediately! Doing otherwise would be unconscionable!”
We’re not seeing that yet, which raises the question of why not. I mean, it’s not like cultural patterns have been getting more traditional since the mid 70’s, so if the problem is environmental … well, you can see whose ox might get gored.
At any rate, the paper is available via Sci-Hub (put in the doi link to search) and the supplement is free via PNAS.
And, sigh. Peer review was a mistake. We need ‘public review’ too. Research transparency now!
This is yet another one of those cases in which it’s hard to understand how ordinary Scientific discourse can even work without the raw data available for wide use scrutiny, to test whether certain statistical manipulations and corrections are fair, robust, etc. This is the model in which publication is supposed to be the reliably trustworthy end of of the conversation, instead of the beginning. That how you got the ‘replication crisis’.
In this case there are some data problems, and the researchers are trying to correct for them, but the whole question is whether those corrections are actually correct.
The three big problems are these:
1. Families with at least two brothers (but not twins) may be different from other families in ways that are hard to correct for. Also in the nature of things, brothers aren’t very far apart in years, so differences between them that are part of larger, social trends working themselves out at fractions of a standard deviation over decades are extremely tiny and not easy to tease out.
2. There’s a birth order effect: IQ tends to go down with subsequent kids (although there is some debate about how much of that is related to age of parents, and even here, is it because of womb environment, changed in use and exposure to certain drugs, or age-related accumulation of mutations – thus bolstering the ‘genetic’ model – or child rearing attention, or something else?)
This is obviously related to problem 1 above. The researchers came up with a model for what should be happened with birth order effects, but based it on what did happen prior to the peak. However, it’s not certain that whatever causes birth order effects on IQ would necessarily stay constant over time or in a different generation.
3. There’s a selection effect. Bottom line: not every kid gets tested, fewer second brothers get tested than they used to across the board, and low-IQ second brothers have been much less likely to be tested.
So you can see the big problem. The question is, do any of the attempts to correct for these issues bias things to produce the observation of what is, in truth, a very small and subtle trend? Is it “really” happening, or is it an erroneous artifact of the mathematical manipulation?
Mystery to me.
I would look at digital, web, handheld. See if less TV more digital correlates.
Then here is the monetary union, people quit thinking, started buying?
Is the Null hypothesis strong?
Dunno, this is something that takes much more looking.
You might also look at this (‘there are subtle issues with the primary data’). https://evoandproud.blogspot.com/2018/06/why-is-iq-declining-in-norway.html.
I am a little dubious on anything happening