Black and white IQs are moderately correlated across regions: General Social Survey (GSS) data show that mean IQ increases for whites in America as we move north. The same is true for blacks: the lowest average is in the East South Central region (ESC), while the highest is West North Central (WNC). I wanted to look at the relationship more closely, so I calculated the Pearson correlation for black and white mean IQs across the nine GSS divisions. It turned out to be .473. The correlation is lowered by the fact that, while whites in the Intermountain West are smarter than average, for some reason blacks are not.
Could it be that smarter southern blacks migrated to the west coast (blacks are above average there) while their duller counterparts got no farther than service jobs in Nevada? (I doubt that blacks are more than 1 or 2 percent, except for places like Vegas and Phoenix).
So how do we explain the moderately strong relationship between black and white IQs? Is there some kind of environmental factor that lowers intelligence in the south? If so, what would it be? (I'm sure Agnostic could help us out here). Or is it migration--more ambitious blacks and whites heading north to pursue better opportunities? (But how many low IQ blacks have been attracted to northern states with generous welfare programs?)
The differences are by no means trivial. The New England/ESC gap for whites is 8 points--more than half a standard deviation. For blacks, the IQ difference between the WNC and ESC regions is also about 8 points. The gap is so wide, ESC whites surpass WNC blacks by only 1 IQ point. (Keep in mind that the IQ test is based on vocabulary, and the GSS overall black-white gap for this kind of test is only 10 IQ points.)