产品替代度是研究分销渠道中生产商层次竞争的关键因素，以前大量的研究都是假设两个生产商之间产品的替代度具有双向性。
Product substitutability is the key factor to study the competition between manufacturers in distribution channels , and which is supposed to have characteristic of " double direction " in most previous studies .
分销渠道层次