In this post, I summarize all that I have learned about the actual test scores of different income levels. In particular, I compare actual psychometric data of seven U.S. economic classes: (1) the homeless, (2) welfare recipients, (3) median Americans, (4) self-made millionaires (5) self-made decamillionaires, (6) self-made billionaires, and (7) self-made decabillionaires, and largely confirm my repeated assertion that average IQ increases by 8-10 points for every ten-fold increase in income, though there may be a few major exceptions to this overall trend. Also, by analyzing the slope of the standardized regression line predicting IQ from income, I find evidence that the true correlation between IQ and income (at least in America) is much higher than the 0.23 reported in a 2006 meta-analysis and even higher than the 0.4 correlation asserted by Arthur Jensen, and may even approach 0.5.
I also find tentative but shocking evidence that the IQ gap between the richest and poorest Americans may exceed an astonishing 70 points!
In this analysis I am limiting myself entirely to test score data so IQ estimates based on ethnic composition or educational achievements of various economic classes are only occasionally mentioned to buttress the actual psychometric results. In several cases, the data is somewhat anecdotal, and speculative statistical inferences are sometimes made.