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private_messaging comments on 2012 Survey Results - Less Wrong
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As one of the sceptics, I might as well mention a specific feature of the self-reported IQs that made me pretty sure they're inflated. (Even before I noticed this feature, I expected the IQs to be inflated because, well, they're self-reported. Note that I'm not saying people must be consciously lying, though I wouldn't rule it out. Also, I agree with your three bullet points but still find an average LW IQ of 138-139 implausibly high.)
The survey has data on education level as well as IQ. Education level correlates well with IQ, so if the self-reported IQ & education data are accurate, the subsample of LWers who reported having a "high school" level of education (or less) should have a much lower average IQ. But in fact the mean IQ of the 34% of LWers with a high school education or less was 136.5, only 2.2 points less than the overall mean.
There is a pretty obvious bias in that calculation: a lot of LWers are young and haven't had time to complete their education, however high their IQs. This stacks the deck in my favour because it means the high-school-or-less group includes a lot of people who are going to get degrees but haven't yet, which could exaggerate the IQ of the high-school-or-less group.
I can account for this bias by looking only at the people who said they were ≥29 years old.* Among that older group, only 13% had a high school education or less...but the mean IQ of that 13% was even higher at 139.6, almost equal to the mean IQ of 140.0 for older LWers in general. The sample sizes aren't huge but I think they're too big to explain this near-equality away as statistical noise. So IQ or education level or age was systematically misreported, and the most likely candidate is IQ, 'cause almost everyone knows their age & education level, and nerds probably have more incentive to lie on a survey about their IQ than about their age or education level.
* Assuming people start university at age 18, take 3 years to get a bachelor's, a year to get a master's, and then up to 7 years to get a PhD, everyone who's going to get a PhD will have one at age 29. In reality there're a few laggards but not enough to make much difference; basically the same result comes out if I use age 30 or age 35 as a cutoff.
Yes, and even without particular expectation of inflation, once you see IQs that are very high, you can be quite sure IQs tend to be inflated simply because of the prior being the bell curve.
Any time I see "undiscriminating scepticism" mentioned, it's a plea to simply ignore necessarily low priors when evidence is too weak to change conclusions. Of course, it's not true "undiscriminating scepticism". If LW undergone psychologist-administered IQ testing and that were the results, and then there was a lot of scepticism, you could claim that there's some excessive scepticism. But as it is, rational processing of probabilities is not going to discriminate that much based on self reported data.