常弹性需求与战略性进口政策

Constant-Elasticity Demand and Strategic Import Policy

本文以常弹性需求为例,考察当本国企业和外国企业在本国市场上进行(可能的)古诺竞争时,最优关税的决定问题。研究表明:(1)尽管常弹性需求满足贸易条件收益,但低关税不一定会提高社会福利。(2)就常弹性需求,最优关税的符号并不能仅由需求函数单独决定,边际成本对最优关税的决定有重要影响。(3)如果在自由贸易下,本国企业能够同外国企业进行古诺竞争,且相对外国企业,本国企业缺乏明显的成本优势,则低关税提高社会福利,最优关税为正;反之,若本国企业具备明显的成本优势,则低关税降低社会福利,自由贸易是最优选择。(4)如果在自由贸易下,外国企业的进入将使得本国企业退出市场,则低关税会降低社会福利。此时,相对外国企业,若本国企业的成本劣势并不严重,则应适当征税以使得本国企业进入市场;反之,若本国企业的成本劣势严重,则应选择自由贸易并由外国企业垄断市场。

The paper takes the constant - elasticity demand for example to discuss the decision of the optimal tariff when the domestic firm and the foreign firm take part in the （possible）Cournot competition in the domestic market. The research show ： （ 1 ） Although the constant - elasticity demand satisfies the terms of trade gain, a small tariff will not necessarily improve the social welfare. （ 2 ） The symbol of the optimal tariff is not solely determined by the demand function, and marginal costs are important to the decision of the optimal tariff. （3） If the domestic firm can make the Cournot competition with the foreign firm in free trade, and the domestic firm lacks obvious cost advantages, a small tariff will improve social welfare and the optimal tariff is positive;on the contrary, if the domestic firm has obvious cost advantage, a small tariff will reduce social welfare and free trade is the best choice. （4） If the entry of the foreign firm will cause the domestic firm to withdraw from the market in free trade, a small tariff will reduce the social welfare. For this case, comparing with the foreign firm, if the cost disadvantage of the domestic firm is not serious, an appropriate tariff should be adopt to make the domestic firm to enter the market;on the contrary, if the cost disadvantage of the domestic firm is serious, it is best to choose free trade and let the foreign firm monopolize the market