There must be some selection effect at work. "Those who live with them" are the ones who have chosen to live with them, which excludes:

a) all who have learnt about the situation before birth and chose abortion,

b) all who gave the kid away to some institution.

A N == 1 case from my life. My classmate had a Down kid at 20 - very rare, as Down is not typical in young mothers. She seems to be happy, even though she sacrificed her dream of a bigger family for him; it was so challenging having a Down kid that she didn't have any other.

But the father absconded and wants nothing to have with his disabled son.

Of course there is, but when the perspective being asked is, "What's it like to raise a child with DS?" the only people who validly have an opinion are parents of kids with DS.

A different N==1, a friend and coworker of mine had a son with DS at 23. He's now the oldest of six children. They're doing great, and he's a terrific big brother.

I think the studies matter because N needs to equal more than 1 to get a sense of how it goes for the people who do it.