 Larry Bartels, a Princeton political scientist and the author of "Unequal Democracy", argues that federal tax policy since 1964 and starting even before that has increased economic inequality in the United States.He states that the real income growth rate for low and middle class workers is significantly smaller under Republican administrations than it is under Democratic administrations while the real income growth rate for the upper class is much larger under Republican administrations than it is for Democratic administrations.He finds that from 1948 to 2005, pre-tax real income growth for the bottom 20% grew by 1.42% while pre-tax real income growth for the top 20% grew by 2%.