Mobility and Mobility Measures

TL;DR

This paper critically evaluates existing mobility measures, proposing three fundamental principles for their assessment and introducing two classes of measures with clear distributional interpretations, linking them to well-known inequality metrics.

Contribution

It introduces a set of elementary principles for evaluating mobility measures and characterizes two new classes of measures aligned with established inequality concepts.

Findings

Many common mobility indices violate fundamental principles.

Class-1 measures relate to generalized entropy and Kolm inequality.

Class-2 measures connect with Gini inequality measures.

Abstract

We examine whether mobility measures appropriately represent changes in individual status, like income or ranks. We suggest three elementary principles for mobility comparisons and show that many commonly used indices violate one or more of them. These principles are used to characterise two classes of measures that have a natural interpretation in terms of distributional analysis. Class-1 measures are based on the summation of power functions of individual status levels and have connections with generalised-entropy and Kolm inequality measures. Class-2 measures are based on the weighted aggregation of individual status changes and have connections with (extended) Gini inequality measures.