Panel data that track the same individuals over time are much more informative than statistical categories that do not correspond to specific people. The Treasury did a study in 2007 that tracked the same individual taxpayers over the age of 25 from 1996 to 2005 and found differing results from what the graph above shows. The results showed that during those years, half of taxpayers moved to a different income quintile, with half of those in the bottom quintile moving to a higher one. About 60% of taxpayers in the top 1% in 1996 no longer stayed in that category by 2005.