A tax that is the same amount for everybody, regardless of income or wealth. Some economists argue that this is the most efficient form of taxation, as it does not distort incentives and thus it has no deadweight cost. This is because each person knows that whatever they do they will have to pay the same amount. It is also cheap to administer, as there is no complex process of measuring each person’s income and assets in order to calculate their tax bill. However, because rich and poor people pay the same, the tax may be perceived as unfair – as Margaret Thatcher found out when she introduced a lump-sum “poll tax”, a decision that was later to play a large part in her ousting as British prime minister.