This would also indicate that the decline is not due to differences from one family to the next--it looks like some change that's affecting society at large.
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Here's a possibility: smarter siblings increasingly avoided taking these tests in the cohort that was born after 1975? This is a military test that supposedly everyone must take, but I'm wondering if that's actually the case.
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Alternatively, people in more recent years are increasingly blowing off the test? Nutrition is also a good possibility. Whatever is causing declines in sperm counts (presumably some chemical exposure?) might be causing other problems.
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Are you looking brainstorming or careful analysis of their stats? Obv idea is that the combination of factors that make ppl good test-takers peaked, then declined
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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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Working on it, hope to post shortly!
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Will be great to see your thoughts.
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Here's a possibility: smarter siblings increasingly avoided taking these tests in the cohort that was born after 1975?
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Random effect? Regression to mean?
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No, looks like something in the environment (nutrition? older parents?) or some kind of sampling change.
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post finished, and just checking it again, but the suppositions you have been considering cannot be identified by this study. All it has done is rule out immigration and dysgenics.
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Do you know why migration is included as a potential environmental factor? Seems to me that it could only act on the environment via the other mechanisms.pic.twitter.com/XBghTMJOrJ
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It is a confounder, usually because immigrants are overall of lower ability against European norms.
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You mean more intelligent, but that's apparently not the answer
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