For most goods and services (normal goods), demand is a function of price. As the price of a normal good increases, the demand for that product is likely to decrease. Price elasticity of demand measures the rate at which demand changes in response to a change in price. Hence, by definition, the price elasticity of demand for a particular product cannot be estimated without an understanding of its demand function.  PARS helps firms uncover their demand functions by utilizing one or a combination of the following techniques: