<P> Changes in demand is depicted graphically by a shift in the demand curve . On the other hand, "quantity demanded" refers to the quantity of goods consumers want for a given price, conditional on the other determinants . "Changes in quantity demanded" is depicted graphically by a movement along the demand curve . </P> <P> The law of demand was documented as early as 1892 by economist Alfred Marshall . Due to the law's general agreement with observation, economists have come to accept the validity of the law under most situations . Furthermore, researchers found that the success of the law of demand extends to animals such as rats, under laboratory settings . </P> <P> Generally the amount demanded of a good increases with a decrease in price of the good and vice versa . In some cases, however, this may not be true . There are certain goods which do not follow this law . These include (Veblen goods) and Giffen goods . Further exception and details are given in the sections below . </P> <P> Initially proposed by Sir Robert Giffen, economists disagree on the existence of Giffen goods in the market . A Giffen good describes an inferior good that as the price increases, demand for the product increases . As an example, during the Irish Potato Famine of the 19th century, potatoes were considered a Giffen good . Potatoes were the largest staple in the Irish diet, so as the price rose it had a large impact on income . People responded by cutting out on luxury goods such as meat and vegetables, and instead bought more potatoes . Therefore, as the price of potatoes increased, so did the quantity demanded . </P>

According to the law of demand what will happen as the price of a good or service decreases
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