A note on measuring multi-product market power using the lerner index
重新审视了Shaffer和Spierdijk关于加总勒纳指数等于产品级勒纳指数加权平均的条件，证明该条件可弱于可分离成本函数与线性产出加总函数的假设。
ABSTRACT In this note we re-examine Shaffer and Spierdijk (2020) conditions for the aggregate Lerner index to be equal to the weighted-average of product-specific Lerner indices and we show that they can be made weaker than assuming a separable cost function with a linear output aggregation function. In particular, we verify that the aggregate Lerner index is equal to the weighted average of the product-specific Lerner indices, with revenue share as weights, if the cost function is separable in outputs and the output aggregation function is linearly homogenous.