Regional Trading Arrangements: Natural or Super-Natural
研究自由贸易区（FTA）的福利效应，发现FTA在中等参数范围内可能有害，而适度优惠有利；若优惠过度则进入“超自然”区域，福利低于最惠国待遇现状。引力模型估计显示世界体系可能已处于该区域。
This paper summarizes recent research by the authors on the effects of tree trade areas (FTAs). Within our model, which emphasizes inter-continental transport costs, several conclusions arise. (1) FTAs are likely to be detrimental over a moderate range of parameter values, even if drawn along natural regional lines. (2) A small margin of preferences for neighbors is beneficial. (3) Optimal preferences depend on the parameters, particularly on transport costs. (4) If preferences are raised futther, they enter the zone of negative returns to regionalization, and eventually the super-natural zone, where welfare is lower than under the MFN status quo. Estimates from the gravity model suggest the world system may already be in the super-natural zone. The core model leaves out many factors. But we have pursued a variety of extensions by now. Perhaps the two most important are generalizing the highly stylized model of trade (to include factor endowments), and relaxing the assumption that the inter-bloc level of tariffs remains fixed. In the latter case, allowing tariffs to be endogenous yields a much more optimistic outlook for the effects of FTAs.