The study, published in the National Tax Journal in 2009, and largely ignored by the mainstream press, found [that] during the period 1987 to 2005…56 percent of those in the lowest income quintile at the beginning of the period had moved to a higher quintile 10 years later. Almost 30 percent went to the second quintile, and 27 percent moved up two or more quintiles. At the end of the 10-year period, 4.5 percent had moved to the top quintile.
Furthermore, many of those in the top quintile do not stay there. Only 40 percent of those in the top quintile in 1996 were there in 2005. Less than a quarter of those who represented the top one percent in 1996 were among that coveted group in 2005.
Data show that 3,672 different taxpayers were in the list of the top 400 returns over the years between 1992 and 2008. Only four returns, or one percent, were found on the list in all 17 years. On average, each year 39 percent of those in the top 400 were not on the list in any other year.
Entire Diana Furchtgott-Roth editorial worth reading.