The issue of socioeconomic status (and social mobility) in relation to IQ is an empirical issue, and it is investigated empirically from time to time. An old article that I somehow missed at the time of publication, but which I coincidentally saw while searching for something else a few days ago, mentions some of the other influences on socioeconomic status besides IQ (that is, "controlling for IQ") in one study sample.
http://www.newscientist.com/article/dn11711-smarter-people-are-no-better-off.htmlThat article confirms my assertion that IQ and income are positively correlated:
On the surface, Zagorsky's analysis confirms the findings of previous studies linking higher intelligence with higher income. "Each point increase in IQ test scores is associated with $202 to $616 more income per year," he says. For example, a person with a score of 130 (in the top 2%, in terms of IQ) might earn about $12,000 more per year than someone with an average IQ score of about 100.
On the surface, people with higher intelligence scores also had greater wealth. The median net worth for people with an IQ of 120 was almost $128,000 compared with $58,000 for those with an IQ of 100.
But when Zagorsky controlled for other factors - such as divorce, years spent in school, type of work and inheritance - he found no link between IQ and net worth. In fact, people with a slightly above-average IQ of 105 , had an average net worth higher than those who were just a bit smarter, with a score of 110.
Finding no link between IQ and wealth (rather than income) when controlling for educational attainment and type of work is not very meaningful, because IQ is a major determining factor of educational attainment and the type of work one does.
Yes, if you have a drop out of high school and work your whole life in a low-skilled job, you probably won't be wealthy, but high-IQ people tend not to be high school dropouts working their whole lives at low-skilled jobs.
