The Lerner symmetry theorem is a result used in

international trade International trade is the exchange of capital, goods, and services across international borders or territories because there is a need or want of goods or services. (See: World economy.) In most countries, such trade represents a significan ...

theory, which states that an

ad valorem An ''ad valorem'' tax (Latin for "according to value") is a tax whose amount is based on the value of a transaction or of a property. It is typically imposed at the time of a transaction, as in the case of a sales tax or value-added tax (VAT). A ...

import tariff A tariff or import tax is a duty imposed by a national government, customs territory, or supranational union on imports of goods and is paid by the importer. Exceptionally, an export tax may be levied on exports of goods or raw materials and is ...

(a percentage of value or an amount per unit) will have the same effects as an export tax. The theorem is based on the observation that the effect on relative prices is the same regardless of which policy (ad valorem tariffs or export taxes) is applied. The theorem was developed by economist Abba P. Lerner in 1936. Jagdish N. Bhagwati,

Arvind Panagariya Arvind Panagariya (born 30 September 1952) is an Indian economist who is holding the position of Jagdish Bhagwati Professor of Indian Political Economy at Columbia University and the Director of Deepak and Neera Raj Center on Indian Econo ...

, and T. N. Srinivasan, 1998 ''Lectures On International Trade'', 2nd Edition, MIT Press
Description
and ch. 12, sect. 12-6, Lerner Symmetry Theorem, scrollable preview, pp
215-19.
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Notes

References

Economics theorems {{econ-stub