in addition it is also important to consider the scale of income tax in particular marginal tax rates at the top of the income scale are an important element in overall progressivity even though the top earners constitute a small segment of the population because they often account fora large share of aggregate income and the total income tax yield yet marginal personal income tax rates at the top of the income scale in oecd countries fell from an average of per cent in the late s to around percent in the late s chart one reason for this was divergent patterns in the taxation of wealth piketty