Measuring Surplus Attributable to Differentiated Products: Reply
作者回应Wildman的批评，承认自己在估算新谷物产品剩余时犯了错误，并扩展了衡量新产品福利贡献的理论，指出测量困难但可通过价格变化和生产者剩余被蚕食的程度来界定可准确测量的情形。
PROFESSOR WILDMAN'S paper performs a double service for which I must express personal and professional appreciation. It correctly identifies an error I made in attempting to estimate the surplus attributable to new cereal products. In effect, I confused how total welfare was affected ex ante by price changes with what one could actually observe ex post. And it greatly extends the theory relevant to measuring new products' welfare contribution. It is disappointing that the measurement problem turns out to be so difficultmuch more so than I assumed in my article. Nevertheless, Wildman's comment also helps identify and place bounds upon the cases in which tolerably accurate measurements can be made-notably, those in which the resulting price changes are zero or small (to which cereals did not conform) and those in which the fraction of producer's surplus cannibalized is high (to which cereals did conform, although not perfectly). It seems clear from Wildman's analysis that I understated the net benefits from new cereal products and hence underestimated the number of new products with positive net welfare contributions. I doubt, however, that the latter estimate was seriously askew, since I found that the (under)estimated benefits from new products tailed off rapidly as one added to the list products with smaller market shares. A sensitivity analysis revealed that raising the surplus estimate by 46 percent increased the number of net welfare-enhancing brands by only 29 percent (from I7 to 22).