隨機與垂直相關市場中的最適貿易政策

Optimal Trade Policy in Vertically and Stochastically Related Markets

本文建立一個三國貿易模型。模型中一家垂直整合且風險趨避廠商出口關鍵性零件給外國廠商生產最終財，並且與之在第三國最終財市場進行數量競爭。我們假設最終財需求函數與關鍵性零件生產過程具有不確定性。我們證明，最終財需求與關鍵性零件生產過程的隨機變數變異程度與相關程度會影響垂直整合廠商供應關鍵性零件給敵對廠商的決策。在自由貿易下，如果兩隨機變數為正相關，垂直整合廠商就不會封殺關鍵性零件供應給敵對廠商的決策。垂直整合廠商的國家應該對其最終財出口課稅，但是在某些狀況下會對其關鍵性零件出口補貼。面對外國關鍵性零件獨占廠商，進口國必須對其最終財出口課稅以提高社會福利。

We build a model in which a vertically integrated (VI) risk-averse firm supplies key inputs to its rival in the final goods market. Two correlated risks occur in the final goods market and input production process. Depending on the variation and correlation of shocks, the VI firm may increase its output to respond to its enemy’s increase in outputs. Under the free trade policy, if random shocks are positively correlated, the VI firm will NOT foreclose the input market. The input-exporting country should always tax its final goods export and may tax or subsidize the input exports. The optimal policy for the input-importing country is to tax the exported final goods to fight against the foreign input monopolist.