Even if every self-reported IQ is exactly correct, the average of the self-reported IQ values can still be (and likely will still be) higher than the average of the readership’s IQ values.
Consider two readers, Tom and Jim. Tom does an IQ test, and gets a result of 110. Jim does an IQ test, and gets a result of 90. Tom and Jim are both given the option to fill in a survey, which asks (among other questions) what their IQ is. Neither Tom nor Jim intend to lie.
However, Jim seems significantly more likely to decide not to participate; while Tom may decide to fill in the survey as a minor sort of showing off. This effect will skew the average upwards. Perhaps not 30 points upwards… but it’s an additional source of bias, independent of any bias in individual reported values.
I remember looking into this when I looked at the survey data. There were only a handful of people who reported two-digit IQs, which is consistent with both the concealment hypothesis and the high average intelligence hypothesis. If you assume that nonresponders have an IQ of 100 on average the average IQ across everyone drops down to 112. (I think this is assumption is mostly useful for demonstrative purposes; I suspect that the prevalence of people with two-digit IQs on LW is lower than in the general population.)
(You could do some more complicated stuff if you had a functional form for concealment that you wanted to predict, but it’s not obvious to me that IQs on LW actually follow a normal distribution, which would make it hard to separate out the oddities of concealment with the oddities of the LW population.)
Select a random sampling of people (such as by picking names from the phonebook). Ask each person whether they would like to fill in a survey which asks, among other things, for their IQ. If a sufficiently large, representative sample is taken, the average IQ of the sample is likely to be 100 (confirm if possible). Compare this to the average reported IQ, in order to get an idea of the size of the bias.
Select a random sampling of lesswrongers, and ask them for their IQs. If they all respond, this should cut out the self-selection bias (though the odds are that at least some of them won’t respond, putting us back at square one).
Even if every self-reported IQ is exactly correct, the average of the self-reported IQ values can still be (and likely will still be) higher than the average of the readership’s IQ values.
Consider two readers, Tom and Jim. Tom does an IQ test, and gets a result of 110. Jim does an IQ test, and gets a result of 90. Tom and Jim are both given the option to fill in a survey, which asks (among other questions) what their IQ is. Neither Tom nor Jim intend to lie.
However, Jim seems significantly more likely to decide not to participate; while Tom may decide to fill in the survey as a minor sort of showing off. This effect will skew the average upwards. Perhaps not 30 points upwards… but it’s an additional source of bias, independent of any bias in individual reported values.
I remember looking into this when I looked at the survey data. There were only a handful of people who reported two-digit IQs, which is consistent with both the concealment hypothesis and the high average intelligence hypothesis. If you assume that nonresponders have an IQ of 100 on average the average IQ across everyone drops down to 112. (I think this is assumption is mostly useful for demonstrative purposes; I suspect that the prevalence of people with two-digit IQs on LW is lower than in the general population.)
(You could do some more complicated stuff if you had a functional form for concealment that you wanted to predict, but it’s not obvious to me that IQs on LW actually follow a normal distribution, which would make it hard to separate out the oddities of concealment with the oddities of the LW population.)
Ah! Good point! Karma for you! Now I will think about whether there is a way to figure out the truth despite this.
Ideas?
Hmmm. Tricky.
Select a random sampling of people (such as by picking names from the phonebook). Ask each person whether they would like to fill in a survey which asks, among other things, for their IQ. If a sufficiently large, representative sample is taken, the average IQ of the sample is likely to be 100 (confirm if possible). Compare this to the average reported IQ, in order to get an idea of the size of the bias.
Select a random sampling of lesswrongers, and ask them for their IQs. If they all respond, this should cut out the self-selection bias (though the odds are that at least some of them won’t respond, putting us back at square one).
It’s probably also worth noting that this is a known problem in statistics which is not easy to compensate for.
There’s also the selection effect of only getting answers from “people who , when asked, can actually name their IQ”.