How can a country's IQ be different of 100, if the average IQ of a population is always 100? [duplicate]

In The Idiot Brain: A Neuroscientist Explains What Your Head is Really Up To, Dean Burnett write that:

"the average IQ of a population is 100. Without exception. If someone says, “The average IQ of [country x] is only 85,” then this is wrong. It's basically the same as saying, “ The length of a meter in [country x] is only 85 cm”; this is logically impossible, and the same is true for IQ." (cf https://books.google.fr)

I think this is misleading. He is right to write that the average IQ of a population is 100 (as explained here). But it doesn't imply that it's "wrong" to say that “The average IQ of [country x] is only 85,”. If one takes the whole word population as the population then one can then calculate the average IQ of the people in a particular country.

But then if it's how countries' IQ are measured, why so few countries have an IQ above 100? There is only 15 countries with an average IQ of 100 or above (the max is 108), and so many countries are below 100, the lowest being 59. Even with China (representing about 20% of the world population) pulling the world average IQ closer to 100, the countries' IQ given on that page are not coherent with an aveage wold IQ of 100.

So how are the countries IQ measure? My question isn't about why the average IQ of a population is always 100 but about the discrepancies between countries.

• Have a read of the concept of Greenwich IQ by the white nationalist Lynn in his book IQ of Nations. Feb 15, 2018 at 16:03
• @chris this seems to be more specific in addressing the discrepancies between countries, so I don't feel it's a duplicate. Feb 15, 2018 at 16:49
• @Chris, I have edited the question and changed the title. As Seanny wrote, the thread you mention doesn't answer my question (the only part dealing with my question is "if you use the UK/US average as a baseline to look at IQ scores around the world" but this is not well explained and it's worded with a "if"). Feb 16, 2018 at 16:21
• Imo the answer is in the dupe. If you can make it more explicit what you wish to know I'm happy to reopen.
– AliceD
Feb 16, 2018 at 23:01