So anyone earning a $1 more than the average is upper class income?
Middle class is a range...it has to be a specific amount above and below the average or median household income (depending on which number you subscribe to).
Well you have to stablish limits to start considering something middle class or upper class, it's silly that only 1 dollar can make the difference but like i said before there must be limits.
If it were actually of importance then it would be something along the lines of being writhing a certain number of standard deviations of the mean wage in the local area.
I would assume that someone earning 100k in New York is poorer as a percentage of the population than someone earning 90k in Idaho.
Just as a side note, in the UK class has no direct link with earnings, it is more of a family history and job title thing.