High Quality Content by WIKIPEDIA articles! Price elasticity of demand (PED) is defined as the responsiveness of the quantity demanded of a good or service to a change in its price. In other words, it is percentage change of quantity demanded by the percentage change in price of the same commodity. In economics and business studies, the price elasticity of demand is a measure of the sensitivity of quantity demanded to changes in price. It is measured as elasticity, that is it measures the relationship as the ratio of percentage changes between quantity demanded of a good and changes in its price. Price elasticity is almost always negative, although analysts tend to ignore the sign. Only goods which do not conform the law of demand, such as Veblen and Giffen goods, have a positive PED.