|Abstract: ||在第二章中，我們利用一個標準的垂直差異化模型來探討在一個封閉經濟體系下，政府最適的政策。我們先建立一基本模型探討未管制下之，廠商進行Bertrand競爭及Cournot競爭時，廠商的最適品質選擇及社會福利。接著分別探討政府的單一品質管制及差別品質管制政策，並比較Bertrand 競爭與Cournot 競爭下的均衡結果。本章發現，在差別管制與單一管制下政府對廠商的最適品質管制政策隨廠商的市場競爭型態不同。若政府採差別品質管制，在Bertrand (Cournot) 競爭下，應分別要求高、低品質廠商提高產品品質（應分別要求高（低）品質廠商提高（降低）產品品質），縮小（擴大）品質差距。若採取單一品質管制，在Bertrand (Cournot) 競爭下，會使兩廠商的產品品質均提高，且低品質廠商生產最低品質標準（應放任廠商自由決定品質）。|
;In Chapter 2, we analyze the optimal uniform and discriminatory quality requirements under Cournot and Bertrand competition when two firms produce high, and low, quality products respectively in a domestic market. We find that under uniform and discriminatory quality requirements, the government’s optimal quality requirement depends on the type of competition in which firms engage. When discriminatory quality requirements are adopted, the government should ask both high and low quality firms to raise their quality standard under Bertrand competition and decrease the quality differentiation. However, the government should ask the high quality and low quality firm to raise and lower their quality respectively and increase the quality differentiation under Cournot competition. When uniform quality requirement is adopted, the government should set a quality requirement raising both firms’ quality respectively under Bertrand competition, and the low quality firm will produce at the lowest quality standard, while under Cournot competition the government should not set any quality requirement. In addition to premium agricultural products seal, our results also provide useful strategic recommendations for the government’s quality policy.
In Chapter 3, we analyze the same issues when two firms produce high-quality and low-quality products, respectively, in an international market. The quality requirements in our paper are not set for the foreign firm but are set to regulate products of different qualities, since in the real world a domestic firm could be a high- or low-quality producer. We find that whether the government should raise the quality requirements depends on the type of competition in which firms engage and the adopted quality requirements. By and large, the government should always set quality requirements raising both firms’ quality directly or indirectly, regardless of the quality of the product of the domestic firm. However, if the domestic firm is a high-quality producer, the government should set a quality requirement that enables the domestic firm to monopolize the market when a discriminatory quality requirement is adopted, and should not set any quality requirement when a uniform quality requirement is adopted. Moreover, we show that the quality requirement can actually improve global welfare in most cases.