看來你和你引文的作者一樣，沒有把household和family的區別搞清楚。

the median household income of $50,054 and divide it up over 12 months, it comes to about $4000 a month.

About half of all American households are making more than that and about half of all American households are making less than that.

So can an average family of four people make it on just $4000 a month?

Well, first of all you have got to take out taxes. After accounting for all forms of taxation you will be lucky if you have $3000 remaining.

上麵是你的引文：

在統計收入時：

Family，即所謂的Census Family，要一個大人和至少另外一個人（大人和小孩）的才算。

統計Household則是按照住址來統計的，一個單身剛工作的算一個household。但是統計family收入時，是不包括隻有一個人的情況的，也就是排除在統計樣本外。

http://www.justice.gov/ust/eo/bapcpa/20110315/bci_data/median_income_table.htm

上麵統計出來的Family Income，4口之家，最窮的州都有$53,709，比你那位作者的$50,054高多了。