中文摘要：

本文采用相对分布非参数核密度估计方法,基于中国健康与营养数据库（CHNS） 1988-2010年居民住户调查微观数据,对影响中等收入群体比重变动的因素进行分解.实证结果显示,一方面,影响中等收入群体比重变动的因素中,“经济增长效应”大于“收入分配效应”,即经济增长所带来的收入分布曲线平移产生的效应大于收入分配政策变化所带来的分布形状变化产生的效应,同时,“收入分配效应”的短期效应大于长期效应;另一方面,向下相对极化指数大于向上相对极化指数,且向下相对极化指数贡献率呈上升趋势.说明从长期看,经济的快速增长使得中等收入群体划分标准提高,而居民收入增加的速度低于经济增长的速度,使得原本的中等收入群体向下落入低收入区间的比重大于向上成为高收入群体的比重,且呈现逐年上升的趋势.

英文摘要：

Based on the residents＇ household survey micro-data of China Health and Nutrition Survey （CHNS） from 1988 to 2010, applying the nonparametric kernel density estimation method of relative distribution, we decompose the factors that affect the proportion variation of the middle-income group in this paper. Empirical results show that： on the one hand, among the factors that affect the proportion variation of the middle-income group, “Economic growth effect” is greater than “income distribution effect” , and there is an increasing trend, that is, the size of the income distribution curve shift caused by economic growth is greater than the changes in the shape brought by the income allocation policy, At the same time, the short-term effect of “income distribution effect” is larger than the long-term effect. On the other hand, the lower relative polarization index is bigger than the upper relative polarization index, and the lower relative polarization index appears upward trend. It shows that, in the long term, rapid economic growth makes the criteria for the classification of middle-income group increased, while the rate of income increase in household is lower than the rate of economic growth, making the original middle-income groups fall down into the low-income group, and the proportion is greater than the group which become high-income group, and showing an increasing trend.