Illustrating income mobility: new measures
借鉴贫困测量的TIP曲线思路，提出收入流动性的TIM曲线和重排序曲线，用新西兰纳税人数据展示这些图形工具如何直观反映收入流动性的发生率、强度和不等性。
Over two decades ago, Jenkins and Lambert demonstrated that alternative measures of poverty could be combined using the ‘Three Is of Poverty’ (TIP) curve; the ‘three Is’ being the incidence, intensity and inequality of poverty. This paper first takes these TIP curve insights and applies them to income growth based measures of mobility, proposing a new ‘Three Is of Mobility’ (TIM) curve. Secondly, the paper proposes new illustrative devices for income mobility measured as positional change, or re-ranking, within the income distribution: labelled ‘re-ranking curves’. Illustrations use data from random samples of New Zealand income taxpayers between 1998 and 2010. These mobility curves represent simple graphical devices that conveniently illustrate the ‘three Is’ properties of income mobility.