外部干预与部分逆向选择--兼论地方保护与假冒伪劣顽症

本文基于Akedof逆向选择理论，通过引入外部干预因素修正，建立了一个能够在有限次交易中达到非零市场均衡的部分逆向选择模型，借以说明我国当前为什么存在规模化且“长生不衰”的劣质商品市场。在本文的模型中，虽然劣质商品市场会在一定程度上通过逆向选择规律的作用而自然萎缩，但由于“地方保护”等非市场因素的干扰，却不会萎缩至零。有时，劣质商品还甚嚣尘上，形成一定的规模。为了说明我们模型的内在合理性，本文以数量补贴影响预算约束为例，说明外部因素能够改变消费者无差异曲线，从而论证了将这种外部干预引入非封闭市场的合理性。

Outside Interference and Partial Adverse Selection: On Local Protectionism and Persistence of Counterfeits

Based on the Akerlof's adverse selection theory, we introduce the idea of outside interference to construct a partial adverse selection model, which can reach the non-zero equilibrium of market within in finite times of trades. It can be used to explain a current phenomenon in our country that the scalable counterfeit markets can be persistent longer and do not wither to zero. In our model, a counterfeit market can naturally decline to a certain extent due to the adverse selection mechanism, but it cannot completely vanish because of some non-market elements such as the local protectionism. Sometimes the inferior merchandise can even roar very much dust on a large scale. To prove our model further we study the influence of quantity subsidy on the budget constrain and then demonstrate how the outside interference element can change the customer curve. These arguments illustrate the reasonability of our model introducing the outside interference element into an open economics.