Local versus Global Assessment of Mobility*
推导了Shorrocks类流动性指数的聚合规则近似式，揭示其规范属性，并开发估计与推断方法。通过美德比较，发现德国底层收入流动性更高且被指数隐含赋予更大权重，解释了德国整体流动性高于美国的原因。
Mobility indices are popular tools designed to quantify the extent of income changes by aggregating “local” distributional change into a “global” scalar according to some rule. For some mobility measures, this aggregation rule is only implicit in their standard definition. We derive an insightful approximation to the (statistical) aggregation rule for the important class of mobility indices introduced by Shorrocks ( Journal of Economic Theory 19 (1978), 376–93) and further generalized by Maasoumi and Zandvakili ( Economic Letters 22 (1986), 97–102), which enables us to characterize their normative properties. We also develop methods for estimation and inference. A substantive empirical contribution emerges from the comparison of mobility between the United States and Germany. Our methods reveal why income mobility is higher in Germany than in the United States: Higher German mobility in the bottom of the distribution is combined with an implicitly higher weighting by the mobility index at the bottom.