買方市場勢力與水平異質產品生產者：隨機異質的偏好

Abstract

本研究提出一個同時兼顧垂直及水平競爭的架構，此架構同時考慮買方及賣方雙向的市場勢力。上游廠商供給下游廠商均質產品，而下游廠商則把這種產品加工成水平異質產品。然而，上游市場並不是完全競爭的，因為上游各家廠商坐落於不同的區位，供應下游廠商的運輸成本並非為零。下游廠商（亦即加工者）同樣散落各地，因此會向距離它最近的上游廠商購買。這種空間特性賦予下游廠商買方的市場勢力，因為它們各自成為許多上游廠商唯一的買家。在下游市場中，每一家生產異質產品的廠商企圖吸引不同偏好的消費者（每一個消費者具有不同的「品牌偏好」）。這種水平差異正是模型中賣方市場勢力的來源。這個模型使我們得以將總的市場勢力（也就是「價差」）分解成來自於賣方以及買方市場勢力兩部分。本研究首先討論一個最簡單的狀況，亦即所有消費者的願意支付價格以及品牌偏好是確定的，廠商則處於Bertrand 的競爭型態。在這個例子中，模型將探究運輸成本、願意支付價格以及品牌偏好對於下游及上游廠商價差所造成的影響。接著我們將研究價差如何受到下列因素的影響：（一）上下游廠商有不同的競爭類型（例如：勾結和Cournot 競爭），（二）消費者的偏好是隨機異質的，（三）不同的市場結構（例如廠商數目以及廠商是否生產一個以上的品牌）。最後，本研究將根據蒐集的資料，比較各種不同情境下的福利水準。此分析之所以重要是因為福利水準經常無法直接從價差推演而來。舉例來說，因為產品差異所帶來的價差提升（並非因為付給上游廠商的價格降低），一般認為將會減少消費者的福利而增進加工者的利潤（因為較高的下游價格）。然而，消費者的福利很可能實際上是有增無減的，因為較高的產品差異會降低消費者的交通成本，而這個效果可能大到足以抵銷較高價格所帶來的影響。

This project proposes a framework of vertical and horizontal competition where market power is bidirectional: there is buyer as well as seller market power. Upstream firms supply a homogeneous product to downstream firms, which, in turn, process it into a horizontally differentiated product. Supply in the upstream market, however, is not perfectly competitive since firms are situated in different localities and transportation costs to any downstream firm are non-zero. Downstream firms (“processors”) are also scattered in different locations and buy from the nearest upstream firms; this spatial configuration grants downstream firms buyer market power as each of them becomes the sole buyer for a handful of upstream firms. Firms in the downstream market compete with each other by producing a differentiated product intended to attract consumers who have heterogeneous preferences (i.e. each consumer has a different “preferred brand”); this horizontal differentiation is the source of seller market power in our model. A main feature of our model is that it allows us to decompose total market power (“the price spread”) into the portion due to seller market power and the portion due to buyer market power. The project will first consider a simplest case where consumers’ willingness to pay and brand preference are deterministic and firms compete in a Bertrand fashion. The model will show impacts of the transportation cost, willingness to pay, and brand preference on downstream and upstream price spreads in this benchmark case. It then studies how the price spread analysis is affected by: 1) other behavioral assumptions about the type of competition (collusion and Cournot) in the downstream and upstream markets, 2) settings of stochastic and heterogeneous consumer preferences, and 3) different market structures (number of firms and whether firms produce more than one brand). Finally, this project will compare welfare across the different scenarios based on data collected. The welfare analysis is important as welfare may not be inferred from the price spread. For example, a price spread increase that is due mostly to product differentiation (rather than to a reduced price paid to upstream firms) is usually thought to reduce consumer welfare and increase processors’ profits (because of higher downstream prices); however, consumer welfare might actually rise as larger product differentiation may reduce all consumers’ travel costs enough to offset the effect of higher prices.