In TEDS, a longitudinal sample of 10K British twins I work with, the correlation between cognitive ability scores at ages 2, 3 or 4 with scores at age 16 is about 0.2. By 7 it is 0.4, by 12 it is 0.6. These are respectively considered small, medium & large effect sizes.
Stuart Ritchie 🇺🇦 @StuartJRitchie
13 Aug 2021
Sorry, but there's no way the absolutely massive IQ difference in this study is real. An average IQ of 100 for kids born before the pandemic compared to an average of 79 during it? No - sorry, just too huge an effect to be plausible. medrxiv.org/content/10.1101/…

Aug 14, 2021 · 4:11 PM UTC

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Replying to @DamienMorris
In your opinion what is the reason of this effect?
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I think it just takes a long time for brains to properly develop. Whatever makes some babies able to e.g. stack 4 blocks on top of each other a few months earlier than other babies has little to do with how well they'll perform on a matrix reasoning or vocabulary test at age 16.
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