I don't know why people keep thinking class is about personal income.

Edit: this is relevant because their evidence that the middle class is shrinking comes in the form of a drop in the share of total income earned that accrues to the middle quintile, from 17% to 15%. That's an interesting result, but it doesn't really say anything interesting about the "middle class". In my book, if you have to go into work every day or you can't pay the mortgage, you're middle class. You have a job, you have secured debt, you own your home, and your income comes from employment. I will bet you that a much larger span of that spectrum, up to and including most of the top 5%, meet that description. Those at the top might be "upper middle" and enjoy a lifestyle that others envy, but that doesn't make them upper class.