Coincidentally I was reading an entry from Ann Barnhardt's blog earlier today. It might shed some light and confirm what I have just suggested:
"The AVERAGE I.Q. amongst Liberians is 67. Anything below 69 is considered severe impairment. Only people who are profoundly mentally retarded, such as with severe Down Syndrome, have lower I.Q. scores, and many folks with milder Down Syndrome actually have I.Q. scores in the 70s and 80s. What we are talking about in Liberia is the AVERAGE IQ of non-impaired human beings. AVERAGE. Which means, by definition, that half the populace is above 67, and half the population is below 67."
She is evidently referring here to a median, rather than a mean average. In support of this claim Ann offered the following study as proof -
http://www.photius.com/rankings/national_iq_scores_country_ranks.html
Looks like we are on the same wavelength.
At least some of them literally are retarded.