Studies by the Urban Institute and the US Treasury have both found that about half of the families who start in either the top or the bottom quintile of the income distribution are still there after a decade, and that only 3 to 6% rise from bottom to top or fall from top to bottom.On the issue of whether most Americans stay in the same income bracket over time, the 2011 CBO distribution of income study reported:Household income measured over a multi-year period is more equally distributed than income measured over one year, although only modestly so. Given the fairly substantial movement of households across income groups over time, it might seem that income measured over a number of years should be significantly more equally distributed than income measured over one year. However, much of the movement of households involves changes in income that are large enough to push households into different income groups but not large enough to greatly affect the overall distribution of income. Multi-year income measures also show the same pattern of increasing inequality over time as is observed in annual measures.In other words,many people who have incomes greater than $1 million one year fall out of the category the next year – but that's typically because their income fell from, say, $1.05 million to .95 million, not because they went back to being middle class.Disagreements about the correct procedure for measuring income inequality continues to be a topic of debate among economists, including a panel discussion at the 2019 American Economic Association annual meeting.