比較利益、異質生產者與內生彈性

COMPARATIVE ADVANTAGE, HETEROGENEOUS FIRMS AND ENDOGENOUS ELASTICITY

結合Heckscher-Ohlin與Melitz（2003）的模型特性，Bernard et al.（2007）（BRS）指出，在僅有部份生產者出口的前提下，貿易自由化透過要素的重新分配，會改變產業間之相對生產力，進而放大稟賦差異所產生的比較利益，BRS將之稱為放大效果（magnification effect）。然而實證上研究比較利益如何隨時間改變的文獻，有些呈現各國間比較利益逐漸放大，有些呈現逐漸縮小的結果。本文指出，若考量競爭對加價的影響，當兩產業之要素密集度差異低於一門檻值時，此放大效果隨貿易自由化非單調（non-monotonically）地變動，反之則單調（monotonic）地變動。數值例子顯示，若是非單調地變動，在自由化程度較低時，進一步自由化強化放大效果，但在程度較高時，該效果隨自由化減弱，並在市場完全融合後消失；反之則放大效果隨自由化逐漸下降並消失。此結果呼應實證發現分歧的現象。雖然BRS亦隱含放大效果之減弱，但此結果伴隨所有生產者出口以及絕對生產力逐漸下降至封閉水準，不符過往實證之發現，因此作者並未加以討論。本模型可在產生非單調關係的同時，在此兩點上滿足過去實證的結果。 Bernard et al. (2007) (BRS) combine the Heckscher-Ohlin model and the mechanism of Melitz (2003) to show that if not all firms export, trade changes relative industrial productivity and magnifies the Heckscher-Ohlin comparative advantage through factor reallocation. This paper shows that depending on the difference in factor intensity between industries, the magnification effect changes monotonically or non-monotonically with trade liberalization when the mechanism comes from the increase in markup. BRS also mention the possibility of non-monotonicity. However, the decrease in magnification effect accompanies the decrease in industrial productivity and the result that all firms export, which does not coincide with empirical findings. In this paper, the non-monotonicity is not based on firms' export decision, and industrial productivity increases during trade liberalization. The ambiguous relationship between liberalization and comparative advantage also coincides with the recent empirical findings.