Since the 1970s, income growth for the richest people and places has far outpaced the relatively modest increases seen elsewhere. In 1980, only about 12 percent of the population lived in places that were especially rich or especially poor. By 2013, it was over 30 percent.

See the source article by following the link below:
Since the 1970s, income growth for the richest people and places has far outpaced the relatively modest increases seen elsewhere. In 1980, only about 12 percent of the population lived in places that were especially rich or especially poor. By 2013, it was over 30 percent.