[T]he middle class is shrinking not just because more people are poor but also because more people are rich. The share of Americans that are in high-earning households, those with more than double the median income, has grown by seven percentage points since 1971. The share of low earners, those earning less than two-thirds the median, has grown just four percentage points. In fact, what Pew calls the “hollowing of the American middle class” is even starker than that: Most of the growth has come at the extreme bottom and top of the income spectrum. In other words, the shrinking of the middle class is less about decline than polarization.