From the CONGRESSIONAL BUDGET OFFICE:
The pattern of average tax rates has varied over time. The lowest three income quintiles have seen steady declines in their average rate. The tax rate on the fourth quintile was flat over most of this period, before declining in the early part of this decade. The tax rate on the top quintile has fluctuated more, with periods of increases and decreases.By the way, since this information comes from the CBO, we should assume that every member of Congress has this information available to him or her, or at least to staff members. So, the next time a member of Congress in on a soapbox opining about taxes on the rich and the poor, you will be able to judge the veracity of the assertions.