He did link to and summarise research on the psychological differences between the sexes - but it seems that this was the cause of quite a bit of the blowback because people didn't understand that this is what he was doing e.g. when he was talking about Neuroticism in the technical sense as one of the big 5 personality traits, and many people incorrectly interpreted that as him calling women neurotic.
Also the links he provided that would have given this context were removed from quite a few of the online copies of the manifesto, causing further confusion.
Also the links he provided that would have given this context were removed from quite a few of the online copies of the manifesto, causing further confusion.