Furthermore, the wealthy often move down the wealth ladder. Needless to say, if this is true, it is good news, indeed. Unfortunately, that is not the case. One of the blessings of the Internet is the ability to check sources, and Sowell usually provides enough clues in his columns to trace the origin of his figures. There is some merit in this position.
Persons usually earn less when they enter the job market than they do later.
A person's retirement income will usually be lower than what they earned prior to retirement. It therefore stands to reason that earnings over a lifetime probably would be a better indicator of economic well-being than a statistical slice of the population at any given time. In many ways, it's like the difference between an earnings statement, which covers a period of time, and a balance sheet, which is a snapshot of the assets and liabilities of a firm at a point in time. Because of difficulties in the collection of data, Cox and Alm dwell upon the period from 1975 to 1991, covering 3,725 individuals. The second source is a 10-year study by the U. S. Treasury of persons who had filed tax returns for 10 consecutive years.