The Rotterdam model can be used to estimate one form of this quantity, for which Richard Stone was the first to empirically derive a linear expenditure system. For a firm in a perfectly competitive market, this quantity is infinitely elastic. The Slutsky equation (10[2])relates the Marshallian form of this quantity (10[1])to its Hicksian form by accounting for the substitution and (10[1])income effects. (10[1])The cross elasticity (10[1])of this quantity measures its sensitivity (10[1])to changes in a different good’s price. For Veblen goods, this quantity (10[1])[emphasize] increases as price increases, often due to the value of those goods as status symbols. For 10 points, what quantity is defined as consumers’ willingness and ability to buy a certain good? ■END■