Kaldor–Hicks efficiency

A Kaldor–Hicks improvement, named for Nicholas Kaldor and John Hicks, is an economic re-allocation of resources among people that captures some of the intuitive appeal of a Pareto improvement, but has less stringent criteria and is hence applicable to more circumstances. A re-allocation is a Kaldor–Hicks improvement if those that are made better off could hypothetically compensate those that are made worse off and lead to a Pareto-improving outcome. The compensation does not actually have to occur (there is no presumption in favor of status-quo) and thus, a Kaldor–Hicks improvement can in fact leave some people worse off. A situation is said to be Kaldor–Hicks efficient, or equivalently is said to satisfy the Kaldor–Hicks criterion, if no potential Kaldor–Hicks improvement from that situation exists. A reallocation is said to be a Pareto improvement if at least one person is made better off and nobody is made worse off. However in practice, it is almost impossible to take any social action, such as a change in economic policy, without making at least one person worse off. Even voluntary exchanges may not be Pareto improving if they make third parties worse off. Using the criterion for Kaldor–Hicks improvement, an outcome is an improvement if those that are made better off could in principle compensate those that are made worse off, so that a Pareto improving outcome could (though does not have to) be achieved. For example, a voluntary exchange that creates pollution would be a Kaldor–Hicks improvement if the buyers and sellers are still willing to carry out the transaction even if they have to fully compensate the victims of the pollution. Kaldor–Hicks does not require compensation actually be paid, merely that the possibility for compensation exists, and thus need not leave each at least as well off. Under Kaldor–Hicks efficiency, an improvement can in fact leave some people worse off. Pareto-improvements require making every party involved better off (or at least none worse off).