Research has shown that in the gifted population, introverts are significantly more common than in the general population. This doesn't mean that all introverts are gifted, but that the two qualities do often correlate.
Also, more than 8 out of 10 National Merit Finalists are N types. This is quite disproportionate to the N types in the general population (2.5 out of 10). Again, this doesn't mean that all N types have high IQs, nor that all people with high IQs are N types, but that N-ness and IQ tend to go together.