The problem with this approach is that each country has a different median income, so the definition of what is middle class shifts from place to place.
这种方法的问题在于每个国家的收入中间值不同，所以中产阶级的定义也就随着地域的不同而有所变化。
2
The first decade of the 21st century was not kind to America's middle class-real median household income was 7% lower in 2009 than it was in 2000.
A philosophy graduate in the Class of 2010, by the way, stands to earn an average starting salary of forty thousand dollars a year, rising to a lifetime median of seventy-six thousand.