Giffen good

In economics and consumer theory, a Giffen good is a product that people consume more of as the price rises and vice versa—violating the basic law of demand in microeconomics. For any other sort of good, as the price of the good rises, the substitution effect makes consumers purchase less of it, and more of substitute goods; for most goods, the income effect (due to the effective decline in available income due to more being spent on existing units of this good) reinforces this decline in demand for the good. But a Giffen good is so strongly an inferior good in the minds of consumers (being more in demand at lower incomes) that this contrary income effect more than offsets the substitution effect, and the net effect of the good's price rise is to increase demand for it. This phenomenon is known as the Giffen paradox. A Giffen good is considered to be the opposite of an ordinary good. Giffen goods are named after Scottish economist Sir Robert Giffen, to whom Alfred Marshall attributed this idea in his book Principles of Economics, first published in 1890. Giffen first proposed the paradox from his observations of the purchasing habits of the Victorian era poor. It has been suggested by Etsusuke Masuda and Peter Newman that Simon Gray described "Gray goods" in his 1815 text entitled The Happiness of States: Or An Inquiry Concerning Population, The Modes of Subsisting and Employing It, and the Effects of All on Human Happiness. The chapter entitled A Rise in the Price of Bread Corn, beyond a certain Pitch, tends to increase the Consumption of it, contains a detailed account of what have come to be called Giffen goods, and which might better be called Gray goods. For almost all products, the demand curve has a negative slope: as the price increases, demand for the good decreases. (See Supply and demand for background.) Giffen goods are an exception to this general rule. Unlike other goods or services, the price point at which supply and demand meet results in higher prices and greater demand whenever market forces recognize a change in supply and demand for Giffen goods.