Over at Human Varieties, Jason Malloy gives a seminar on the the difficulties and methods of calculating the average IQ for a single country. He works through two dozen scientific papers involving IQ in Jamaica, a small English-speaking country with a not undeveloped academic infrastructure.
Many of the IQ scores come from studies of social science interventions, where the test group are a few dozen disadvantaged people with problems and they are compared to a control group of (hopefully) representative Jamaicans. Other IQ tests were done on advantaged populations (e.g., college students, a school in Montego Bay rather than in the Government Yard in Trenchtown, that sort of thing). Jason concludes:
There is no One True Way to do this, and different methods will have different limitations. An average of all the scores will include many samples that were deliberately chosen for health problems (The median IQ of all the samples in the table is 75). I’ve rated the samples for quality to help limit the influence of less representative test groups. 18 of the 41 samples were disadvantaged, 5 of the samples were advantaged, and 18 were reasonably representative. The median IQ of the disadvantaged samples was 66, while the median IQ of the advantaged samples was 87.
The median of 18 reasonably representative samples gives us an IQ of 80 for Jamaica. This is also consistent with Samms-Vaughan (2005 ), one of the more recent and methodologically robust studies, which shows an average IQ of about 81.
So that's quite a bit higher than the 72 Richard Lynn came up with 11 years ago in IQ and the Wealth of Nations. (Malloy discusses the problems Lynn ran into). As I pointed out in my review in 2002, Lynn's low scores for black countries suggest the importance of nurture, not just nature in determining average IQ. Since African-Americans average about 85 and they are about 80% black, then this suggests that environmental forces are holding down black IQs in the third world.
On the other hand, reanalysis over the last decade has tended to come up with somewhat higher scores, which, paradoxically, tend to lessen the likely power of nurture on IQ.
On the third hand, Jamaica is not a dirt poor country: in nurture terms, it's healthy enough, rich enough, and smart enough to do whatever it is that helps a country win Olympic sprinting medals.
It would be interesting to see whether there's enough research on the small island of Barbados to come up with a reliable IQ comparison to Jamaica. There has always been a stereotype of Barbados as more educated and genteel than Jamaica, but does it show up in the data?