Tuesday, March 04, 2008

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.)


  1. I think it's mostly pathogen load, which likely tracks how stable vs. how unstable the environment is. Also latitude, and probably altitude.

    Basically, these types of environments select for migratory features in insects, which are vectors of chronic infectious diseases. They likely select for migratory features in other disease vectors.

    Here are my two GNXP posts on climate and degree of civilization:

    Winged insects and climate

    Data on climate and civiliization

  2. Hmm, that first link doesn't work. Click on the second link, and the first link in *that* post goes to the "winged insects" post.

  3. The further north a state is located, the higher its IQ tends to be.

    That is clearly the global trend at the national level. Distance from the equator and IQ correlate at a statistically significant .67 using data from Vanhanen and Lynn's IQ and the Wealth of Nations. The relationship is more rigorous even than the contemporary relationship between purchasing power parity and IQ (as an aside, life expectancy shows the single strongest correlation with IQ at .85, followed by infant mortality at an inverse .84, and then--without Mike Judge's endorsement--an inverse relationship with fecundity at .81).

    The trend also holds at the state level within the US. Using the latitude of each state's most populous city and comparing it with estimated IQ yields a correlation of .70, made considerably stronger (.81) if only the lower forty-eight are considered. As the relationship is at the global level, much of this is attributable to race, with blacks concentrated in the Deep South and Hispanics in the Southwest.

    More interestingly, the relationship between latitude and IQ firmly exists in the US when only whites or only blacks are considered. And the correlations are almost identical: .52 for whites (click here for visual representation of estimated white IQ by state) and .51 for blacks (here for visual).

    Insightful post. I'm going to look at the relationship of NAEP scores (the basis for the IQ estimates) by race within states with that prodding.

  4. The coasts have their colleges to siphon off smart people. There aren't more than a few top-tier schools in the South (Duke, maybe Vanderbilt), but both Harvard and MIT are in the same small town in Massachusetts.

  5. But why do elite institutions thrive in temperate or cold climates? Silicon Valley didn't exist very long ago, while the South has been Europeanized for centuries. Hell, Washington state has more going for it than the entire Southeast.

    As you point out, North Carolina is as far south as high civilization can penetrate, and Texas is as far east among southern-latitude states. There really does seem to be some barrier in the southeast.

  6. Maybe the warm weather makes people sleepy?

    Seriously, though, I wouldn't try to explain the pattern of civilization based on the United States; heck, Greece is pretty warm, and they started Western Civ. The South has its own problems which arise out of a history of slave labor and under-industrialization and you could probably find similar areas around the world. That said there probably is some sort of a pattern where the tropics do have too high a pathogen load and the warm weather discourages hard work.

    But you can't make generalizations about the world based on the USA.


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