I'm not addressing the claim of this article, just the methods.
IQ has a misleading (and factually inaccurate) name. The Q stands for quotient, but an actual IQ is not a quotient at all. IQs are ordinal ONLY. They allow you (to the extent that IQ tests measure intelligence) to rank people, not assign numerical values. It is not possible from IQ scores to say "Alice is x% more intelligent than Bob", only "Alice is more intelligent than Bob".
Due to the non-cardinal nature of IQ scores, the correlation with income as reported in the article isn't something that you can really do. To do this, we would need a cardinal measurement of intelligence instead.
Also, IQ tests become less accurate in the outer deviations. Just about impossible to test for a difference between 140 to 150 IQ, or 60 to 70. How much sleep a person got and their diet can change a brain's plasticity by more than that number of points.
IQ tests aren't a great measure of plasticity in the first place - they're just the best thing we have to measure on a wide scale. Plasticity is a far more personal attribute. Many IQ tests just repeat the same problems, and a person can improve their score without really learning anything but how to take an IQ test.
Throw someone something entirely new and you may get real insight into their mental plasticity.
Misconception: The IQ is a direct measure of brain performance. For example, somebody with an IQ of 120 can do 20% more mental work in the same amount of time than somebody with an IQ of 100.
In truth the IQ is a purely statistical measure. It has no direct relation to brain performance, is not proportional to it, and doesn't even have any linear or otherwise straightforward relation to it. The only thing you can say is that somebody with a higher IQ will show higher scores on most other brain performance tests as well, but the IQ doesn't say how much higher.
To clarify: My comment is in support of the parent. Could the downvoters please explain what they think is wrong that I add MORE information and a link to an extended explanation??
IQ has a misleading (and factually inaccurate) name. The Q stands for quotient, but an actual IQ is not a quotient at all. IQs are ordinal ONLY. They allow you (to the extent that IQ tests measure intelligence) to rank people, not assign numerical values. It is not possible from IQ scores to say "Alice is x% more intelligent than Bob", only "Alice is more intelligent than Bob".
Due to the non-cardinal nature of IQ scores, the correlation with income as reported in the article isn't something that you can really do. To do this, we would need a cardinal measurement of intelligence instead.