依循晚近的研究，本計畫試圖建構貿易與所得不均度間的因果關係。國際貿易學者仍 在此議題上有所爭論。類似近幾年的理論及實證上的研究，本文強調貿易與所得不均 度間存在著反「U」型的關係。在資本市場存在摩擦的假設下，生產者的異質性以及要 素在產業內的重分配產生了上述現象。資本市場的摩擦內生的促成了生產力的異質 性。貿易對需求彈性的影響取決於相對生產力，因此當生產者存在異質性時，貿易會 非對稱的影響彈性。因為富有且高生產力的生產者的需求彈性較不受競爭程度的影 響，貿易迫使低生產力的窮人退出市場，並使要素往高生產力的富人集中。然而，當 所有的窮人都退出市場時，競爭對彈性的影響集中於富人身上，因此富人的利潤開始 隨開放程度下降，而貿易也開始減少所得的不均度。 Based on the recent understanding of the nature of international trade, the purpose of this proposal is to establish a plausible causal link between trade and inequality, a debate among trade economists. Similar to the recent theoretical and empirical studies on this topic, this research tries to show a hump-shaped relationship relying on firm heterogeneity and the reallocation of factors within an industry caused by trade. Firms are endogenously different in productivity because they are different in capital endowment. The latter becomes a reason to cause heterogeneity when there are frictions in capital market. Demand elasticity is a function of relative productivity so trade has asymmetric impact on it when there is firm heterogeneity. Trade increases inequality because demand elasticity faced by high-productivity producers who are wealthy is less sensitive to the increase of competition introduced by trade, which forces low-productivity and poor agents to exit and causes reallocation of market share toward wealthy agents. However, when all poor agents have exited, firms are homogeneous and the impact of increasing competition is concentrated on wealthy agents. Therefore, their profit and income inequality start decreasing with degree of trade liberalization.