中国玉米出口地理集中度的优化

The Optimization of Export Geographic Concentration of China’s Corn

摘要: 如果以稳定商品出口为目标，出口地理集中度的优化至少应考虑每个出口市场的波动风险。马科维茨的均值–方差方法为此问题提供了一条解决途径。自2005年以来，中国玉米的出口数量总体上趋于快速下降。为了降低中国玉米出口增长率的波动水平，可以借鉴马科维茨模型的方法，同时使用相对方差衡量波动风险并构建出口市场组合模型。根据该模型和2005~2011年的中国玉米出口数据，本文计算了玉米出口市场的有效组合，以及对应于不同预期出口增长率的地理集中度。地理集中度与市场风险之间不存在简单的线性关系。而最优地理集中度的选择，取决于政策制定者的风险偏好。

Abstract: Taking stabilizing exports as a goal, in order to optimize export geographic concentration, we should consider volatility risk in each export market. The method of Mean-variance of Markowitz provides a solution for this problem. Since 2005, export volume of China’s corn has showed a falling tendency and obvious volatility. This paper learns from Markowitz model and then constructs an export market mix model available to stabilize export growth rate. According to this model and the data on China’s export between 2005 and 2011, we calculated the effective mixes of China's corn export markets and further obtained the varied geographic concentration corresponding to different expected growth rates of exports. The policy makers will select the optimal geographic concentration in the light of their attitude towards risk.