I find this subject a difficult one to quantify as intelligence is extremely variable. In that a person can be extremely well educated but not intelligent emotionally (just one example).
Also I find it a little odd that statistics can be provided without meeting every woman who has chosen to have children and measure their ‘intelligence’ individually.
My IQ is rather high, but I’m dyslexic and discalculic, so to most I appear less intelligent. Also I read a study regarding IQ and it’s representation of actual intelligence and the suggestion was that, whilst they can help gauge certain aspects of cognitive function, they are not able to deduce a person’s individual intelligence.
I do wonder why the need to compare those who don’t have children to those who do, exists. It is by choice either way (in the context of this conversation, I don’t want to minimilise those who aren’t able to conceive).
Also, whilst Idiocracy is a fun film it is not a documentary (I know you know that) I have seen extremely bright children come from families who do no fit the ‘intelligent’ image.
My own Mum who is rather softly spoken comes across to many as less intelligent than her children, my MIL once joked that my sister and I must have been swapped at birth. I corrected her and said that “just because she doesn’t speak in the same way as Dsis and I, does not mean she is stupid. She’s actually very clever, just not in a way that can be displayed or measured by a stranger who barely knows her.”