nonresident with respect to certain income by withholding such tax from such payments and remitting the tax to the government. Such levies are generally referred to as withholding taxes. These requirements are induced because of potential difficulties in collection of the tax from nonresidents. Withholding taxes are often imposed at rates differing from the prevailing income tax rates. Further, the rate of withholding may vary by type of income or type of recipient. Generally, withholding taxes are reduced or eliminated under income tax treaties (see below). Generally, withholding taxes are imposed on the gross amount of income, unreduced by expenses. Such taxation provides for great simplicity of administration but can also reduce the taxpayer's awareness of the amount of tax being collected. Treaties Tax treaties exist between many countries on a bilateral basis to prevent double taxation (taxes levied twice on the same income, profit, capital gain, inheritance or other item). In some countries they are also known as double taxation agreements, double tax treaties, or tax information exchange agreements (TIEA). Most developed countries have a large number of tax treaties, while developing countries are less well represented in the worldwide tax treaty network. The United Kingdom has treaties with more than 110 countries and territories. The United States has treaties with 56 countries (as of February 2007). Tax treaties tend not to exist, or to be of limited application, when either party regards the other as a tax haven. There are a number of model tax treaties published by various national and international bodies, such as the United Nations and the OECD. Treaties tend to provide reduced rates of taxation on dividends, interest, and royalties. They tend to impose limits on each treaty country in taxing business profits, permitting taxation only in the presence of a permanent establishment in the country. Treaties tend to impose limits on taxation of salaries and other income for performance of services. They also tend to have "tie breaker" clauses for resolving conflicts between residency rules. Nearly all treaties have at least skeletal mechanisms for resolving disputes, generally negotiated between the "competent authority" section of each country's taxing authority. Anti-deferral measures Residency systems may provide that residents are not subject to tax on income outside the jurisdiction until that income is remitted to the jurisdiction. Taxpayers in such systems have significant incentives to shift income outside its borders. Depending on the rules of the