Typically, TPC measures the impact of tax laws and proposals in terms of average tax rates. This gives a good measure of how taxes affect our pocketbooks, but economists also like to examine how taxes affect economic incentives. For that purpose, the effective marginal tax rate is most apt. That is, how much tax do we pay on an additional dollar of income. This is important because marginal rates affect the incentive to work that extra hour or to engage in tax avoidance.    more »