A Note on Measuring Surplus Attributable to Differentiated Products
指出Scherer在衡量新谷物产品福利贡献时，忽略了价格上升带来的生产者剩余增加，导致其剩余估计可能偏低而非偏高，并用空间模型和代数推导证明这一点。
IN A RECENT article in this journal, F. M. Scherer [i] presented a study, both analytical and empirical, of the welfare economics of brand proliferation in the ready-to-eat cereal industry. Comparing estimates of contributions to surplus for new products with launching costs, Scherer concluded that during the period I958-70 most new cereal products were introduced at a net cost to society. Scherer's measure of a product's contribution to surplus is the consumer's surplus portion of the area under what he calls a ceteris paribus demand function (hereafter abbreviated as c.p.), the demand function for a single product holding the availability and prices of other products constant. Explicitly ignored in the calculation was the effect of price increases that generally accompanied the introduction of new products. Since consumers' surplus is reduced by an increase in price, Scherer felt that his estimates probably overstated new product benefits. Using a spatial model like the one employed by Scherer in the analytical portion of his paper, I show in Section II that while Scherer's measure does ignore lost consumer surplus due to price increases, and thus overstates the benefits to consumers, also ignored in Scherer's measure is an increase in producer surplus due to higher prices coupled with the appearance of new product variants. The net effect of the two omissions is ambiguous, leaving open the possibility that Scherer's measure of surplus is actually biased downward instead of upward as he supposes. An algebraic exercise reported in Section III shows that Scherer's measure underestimates a product's contribution to surplus if individual demand functions are linear in price and a spatial measure of product differences. Possible uses of c.p. demand functions for estimating the marginal benefits of differentiated products are discussed in Section IV.