therefore, do not lead to economic distortions. However, poll taxes are very unpopular because poorer people pay a higher proportion of their income than richer people. In addition, the supply of people is in fact not fixed over time: on average, couples will choose to have fewer children if a poll tax is imposed. The introduction of a poll tax in medieval England was the primary cause of the 1381 Peasants' Revolt. Scotland was the first to be used to test the new poll tax in 1989 with England and Wales in 1990. The change from progressive local taxation based on property values to a single-rate form of taxation regardless of ability to pay (the Community Charge, but more popularly referred to as the Poll Tax), led to widespread refusal to pay and to incidents of civil unrest, known colloquially as the 'Poll Tax Riots'. Other Some types of taxes have been proposed but not actually adopted in any major jurisdiction. These include: Bank tax Financial transaction taxes including currency transaction taxes Descriptive labels Ad valorem and per unit An ad valorem tax is one where the tax base is the value of a good, service, or property. Sales taxes, tariffs, property taxes, inheritance taxes, and value-added taxes are different types of ad valorem tax. An ad valorem tax is typically imposed at the time of a transaction (sales tax or value-added tax (VAT)) but it may be imposed on an annual basis (property tax) or in connection with another significant event (inheritance tax or tariffs). In contrast to ad valorem taxation is a per unit tax, where the tax base is the quantity of something, regardless of its price. An excise tax is an example. Consumption Consumption tax refers to any tax on non-investment spending and can be implemented by means of a sales tax, consumer value-added tax, or by modifying an income tax to allow for unlimited deductions for investment or savings. Environmental This includes natural resources consumption tax, greenhouse gas tax (Carbon tax), "sulfuric tax", and others. The stated purpose is to reduce the environmental impact by repricing. Economists describe environmental impacts as negative externalities. As early as 1920, Arthur Pigou suggested a tax to deal with externalities (see also the section on Increased economic welfare below). The proper implementation of environmental taxes has been the subject of a long-lasting debate. Proportional, progressive, regressive, and lump-sum An