Grandparent might mean median individual income instead (since household income graphs can be skewed by more people working - Elizabeth Warren writes about this

Grandparent might mean median individual income instead (since household income graphs can be skewed by more people working - Elizabeth Warren writes about this in the Two Income Trap): https://fred.stlouisfed.org/series/MEPAINUSA672N https://fred.stlouisfed.org/series/MEPAINUSA672N