I'm surprised by this recent Norway IQ study. Before 1975, later born children within a family scored higher. After, later born children scored lower. Unless I'm missing something, dysgenics shouldn't play a role here. What happened?
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The even-more-obv solution they claim to exclude (but idk how yet) is eugenic conditions became dysgenic post 1975
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(from the abstract they claim they excluded a selection effect but idk how - you can’t compare 1st/2nd kids for families that don’t have more kids)
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Siblings in the same family should average out to the same genetic potential IQ
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i fall for frequentist traps all the time but: if i have a family, 1 kid, iq=x, and the avg iq of families that have >1 kid =y, shouldn’t reversion put 2nd kid’s iq b/w x & y ?
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Not sure what you mean. What I meant is that kid 1 and kid 2 should receive some random assortment from the same set of genes so aside from the possibility of more mutational load in kid 2 their expected IQ from genetics should be the same.
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but under eu/dys-genic conditions, the mere fact that there is a second kid provides you with additional info about mean familial traits
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ok I see what you mean. Sure, the people with more kids may be dumber, but this is still comparing kid 1 to kid 2 to kid 3 within each family. If we take kid 1 minus kid 2 for each family, we get a set like +5,-7,+3 etc. If we average that out we expect approx zero
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Or maybe it could go like this: All parents have 100 IQ Every set has one kid. 50% 120 IQ, 50% 80 IQ. All parents with 120 IQ kid have another. Parents with 80 IQ kid stop. Second kid has same probabilities. Data set averages to 20 point drop from kid 1 to kid 2
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