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Nornagest comments on 2012 Survey Results - Less Wrong
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Comments (640)
It seems implausible to me that education level would screen off the same parts of the IQ distribution in LW as it does in the general population, at least at its lower levels. It's not too unreasonable to expect LWers with PhDs to have higher IQs than the local mean, but anyone dropping out of high school or declining to enter college because they dislike intellectual pursuits, say, seems quite unlikely to appreciate what we tend to talk about here.
Upvoted. If I repeat the exercise for the PhD holders, I find they have a mean IQ of 146.5 in the older subsample, compared to 140.0 for the whole older subsample, which is consistent with what you wrote.
How significant is that difference?
I did a back-of-the-R-session guesstimate before I posted and got a two-tailed p-value of roughly 0.1, so not significant by the usual standard, but I figured that was suggestive enough.
Doing it properly, I should really compare the PhD holders' IQ to the IQ of the non-PhD holders (so the samples are disjoint). Of the survey responses that reported an IQ score and an age of 29+, 13 were from people with PhDs (mean IQ 146.5, SD 14.8) and 135 were from people without (mean IQ 139.3, SD 14.3). Doing a t-test I get t = 1.68 with 14.2 degrees of freedom, giving p = 0.115.
It's a third of a SD and change (assuming a 15-point SD, which is the modern standard), which isn't too shabby; comparable, for example, with the IQ difference between managerial and professional workers. Much smaller than the difference between the general population and PhDs within it, though; that's around 25 points.
I was really asking about sample size, as I was too lazy to grab the raw data.