In this work we construct a mobility index able to grasp the prevailing direction in the evolution of a given set of statistical units. We consider the case of dynamics ruled by a transition matrix, whose states are based on an ordered economic variable (firm size or income, among others) such that the future position of an individual can be better or worse than the current one. The existing indices measure only the absolute value of mobility, without providing information about the main direction in the dynamics. We propose here a whole family of directional indices defined as functions of the transition matrix, so that their absolute value measures the intensity of mobility, and their sign (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">$$+/-$$</EquationSource> <EquationSource Format="MATHML"> <math xmlns:xlink="http://www.w3.org/1999/xlink"> <mrow> <mo stretchy="false">+</mo> <mo stretchy="false">/</mo> <mo stretchy="false">−</mo> </mrow> </math> </EquationSource> </InlineEquation>) represents the prevailing direction towards improvement/worsening in the dynamics under study. Copyright Springer-Verlag Berlin Heidelberg 2013
