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.
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.
And I suspect if you look at the American population for that age cohort, you’ll find a lot higher a percentage than 13% which have a “high school education or less”… All you’ve shown is that of the highschool-educated populace, LW attracts the most intelligent end, the people who are the dropouts for whatever reason. Which for high-IQ people is not that uncommon (and one reason the generic education/IQ correlation isn’t close to unity). LW filters for IQ and so only smart highschool dropouts bother to hang out here? Hardly a daring or special pleading sort of suggestion. And if we take your reasoning at face-value that the general population-wide IQ/education correlate must hold here, it would suggest that there would be hardly any autodidacts on LW (clearly not the case), such as our leading ‘high school education or less’ member, Eliezer Yudkowsky.
All you’ve shown is that of the highschool-educated populace, LW attracts the most intelligent end, the people who are the dropouts for whatever reason.
Right, but even among LWers I’d still expect the dropouts to have a lower average IQ if all that’s going on here is selection by IQ. Sketch the diagram. Put down an x-axis (representing education) and a y-axis (IQ). Put a big slanted ellipse over the x-axis to represent everyone aged 29+.
Now (crudely, granted) model the selection by IQ by cutting horizontally through the ellipse somewhere above its centroid. Then split the sample that’s above the horizontal line by drawing a vertical line. That’s the boundary between the high-school-or-less group and everyone else. Forget about everyone below the horizontal line because they’re winnowed out. That leaves group A (the high-IQ people with less education) and group B (the high-IQ people with more).
Even with the filtering, group A is visibly going to have a lower average IQ than B. So even though A comprises “the most intelligent end” of the less educated group, there remains a lingering correlation between education level and IQ in the high-IQ sample; A scores less than B. The correlation won’t be as strong as the general population-wide correlation you refer to, but an attenuated correlation is still a correlation.
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.
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.
It’s not too unreasonable to expect LWers with PhDs to have higher IQs than the local mean,
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.
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.
Even before I noticed this feature, I expected the IQs to be inflated because, well, they’re self-reported
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.
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.
And I suspect if you look at the American population for that age cohort, you’ll find a lot higher a percentage than 13% which have a “high school education or less”… All you’ve shown is that of the highschool-educated populace, LW attracts the most intelligent end, the people who are the dropouts for whatever reason. Which for high-IQ people is not that uncommon (and one reason the generic education/IQ correlation isn’t close to unity). LW filters for IQ and so only smart highschool dropouts bother to hang out here? Hardly a daring or special pleading sort of suggestion. And if we take your reasoning at face-value that the general population-wide IQ/education correlate must hold here, it would suggest that there would be hardly any autodidacts on LW (clearly not the case), such as our leading ‘high school education or less’ member, Eliezer Yudkowsky.
Right, but even among LWers I’d still expect the dropouts to have a lower average IQ if all that’s going on here is selection by IQ. Sketch the diagram. Put down an x-axis (representing education) and a y-axis (IQ). Put a big slanted ellipse over the x-axis to represent everyone aged 29+.
Now (crudely, granted) model the selection by IQ by cutting horizontally through the ellipse somewhere above its centroid. Then split the sample that’s above the horizontal line by drawing a vertical line. That’s the boundary between the high-school-or-less group and everyone else. Forget about everyone below the horizontal line because they’re winnowed out. That leaves group A (the high-IQ people with less education) and group B (the high-IQ people with more).
Even with the filtering, group A is visibly going to have a lower average IQ than B. So even though A comprises “the most intelligent end” of the less educated group, there remains a lingering correlation between education level and IQ in the high-IQ sample; A scores less than B. The correlation won’t be as strong as the general population-wide correlation you refer to, but an attenuated correlation is still a correlation.
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.
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.