There is a huge definitional challenge here. For more on that see https://slatestarcodex.com/2019/02/25/wage-stagnation-much-m...

I seldom see addressed how they factor changes in group composition. If the 1% are a constantly changing bunch, the narrative is very different than if it's always the same group of people. I wonder if age composition also has something to do with it (I imagine retiree income differences are much more stark than at 30y)