For several years, just about everyone has implicitly equated the median household’s performance with middle-class performance.
Why?
Well, let’s face it: with no official definition of middle class, it’s easy (and plausible) to assume that as the median household goes, so goes the middle class.
It’s easier, anyway, than going to the trouble of defining the range of households that comprises the middle class, defining the range that comprises the rich, defending those two definitions, calculating the income growth rates for those two ranges, then, finally, comparing the results.
Just hanging our hats on the median household and calling it “the middle class” is a much quicker path to judgment about the success or failure of the policies of the past.
Unfortunately, relying on the median as a proxy for the “middle class” can lead to false conclusions about past policies—which in turn can lead to misguided future policies.
http://www.american.com/archive/2011/september/middle-class