L'américain Thomas Sowell, sur les niveaux de revenus et la mobilité sociale :

Anyone who follows the media has probably heard many times that the rich are getting richer, the poor are getting poorer, and incomes of the population in general are stagnating. Moreover, those who say such things can produce many statistics, including data from the Census Bureau, which seem to indicate that. On the other hand, income tax data recently released by the Internal Revenue Service seem to show the exact opposite: People in the bottom fifth of income-tax filers in 1996 had their incomes increase by 91 percent by 2005. (...)
The top one percent -- "the rich" who are supposed to be monopolizing the money, according to the left -- saw their incomes decline by a whopping 26 percent. Meanwhile, the average taxpayers' real income increased by 24 percent between 1996 and 2005.