Share of income
The middle class is being dismantled by economic forces. More Americans find that they are working in the low wage economy that is booming. For most households income does matter because this is how you finance your life. The Fed has created a system where savers are punished. Negative interest rates punish traditional savings. It makes stocks, junk bonds, and other speculative items seem more lucrative. Those that take on big levels of debt are encouraged. So it is no surprise then that all items financed by debt are suddenly going up in price: housing (mortgages), college (student debt), and cars (auto debt). Yet the larger gains are not trickling down to workers.
Take a look at this chart showing the share of income earned by the top 1 percent: