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Clavus Giulio's avatar

Always great to see this discussed. IQ is less like height and more like mountains - rarefied tall outliers skew the average height up, obscuring the many minute foothills. Similar writings by Nassim Taleb, and which align with my own experience, suggests a skew even more extreme than presented here.

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Chris67's avatar

The left tail theory is supported by the iq distributions of siblings and co-twins when one has mild vs severe ID(the large swedish and israeli studies were posted by cremieux on twitter). It's just the case that most severe ID(and to some extent mild) cases are the result of a developmental issue in a gentile white american population. And the frequency is roughly the same in populations, so I wonder if differences in the standard deviation can be explained by that. But I'm not sure this explains SLODR, if anything mentally disabled individuals have a lower g loading/measurement non-invariance(https://www.research.unipd.it/bitstream/11577/3196682/1/Giofr%C3%A8%2C%20D.%2C%20%26%20Cornoldi%2C%20C.%20(2015).%20The%20structure%20of%20intelligence%20in%20children%20with%20specific%20learning%20disabilities%20is%20different%20as%20compared%20to%20typically%20development%20children.%20Intelligen.pdf). Height has roughly the same distribution as intelligence with a left tail, and similarly rare cases of gigantism/savants have minimal impact on the distribution.

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