Really!! Due to the way in which peoples earnings change over time the only reason this number would not be ~50% is that most elderly with grown children do not have large incomes.
Don't ask me why they couldn't manage to get enough data from those economic backwaters (!) Japan and Australia.
Politically incorrect results maybe?
Regarding Japan I haven't a clue but I have no reason to suspect Austrlia would be finish than either the US or UK. I'm just puzzled by its ommission.
PS - how did I manage to spell 'nation' as 'action'? Must be my hopeless upbringing!