关键词: 中等收入者, 对数正态分布, 因素分解

Abstract: According to constant price and an absolute standard, Changing weights of middle-level income group(MLIG) determined mainly by income growth effect and income distribution effect, By analyzing the impact mechanism of two effects found that income growth will not necessarily lead to increased proportion of MLIG, the widening income gap will not necessarily lead to reduced proportion of MLIG, the direction and degree of two effects affection depends on the medium income division standard’s position on the income density curve. In this paper, the author uses the lognormal distribution to fit Chinese residents' income data and confirm above conclusions.

Key words: Middle-Level Income Group, Lognormal Distribution, Decomposition