Economic Theory 16, 313–321 (2000) The measurement of structural differences between economies: An axiomatic characterization ⋆ Guang-Zhen Sun 1,2 and Yew-Kwang Ng 1 1 Department of Economics, Monash University, Clayton, Victoria 3168, AUSTRALIA 2 Max Planck Institute for Research into Economic Systems, Kahlaische Strasse 10, 07745 Jena, GERMANY (e-mails: sun@mpiew-jena.mpg.de; kwang.ng@buseco.monash.edu.au) Received: September 3, 1999; revised version: November 9, 1999 Summary. In empirical studies concerning comparison of economic structures and/or structural changes of economies, it is quite useful to employ an aggre- gate index to describe the structural difference (similarity). This paper offers an axiomatic characterization of the measurement of structural difference between economies that leads to some difference (similarity) index which is practically useful in empirical studies. Keywords and Phrases: Axiomatic approach, Structural difference (similarity) index, Invariance of proportional sub-classification. JEL Classification Numbers: C43; C40. 1 Introduction In empirical studies concerning the international or inter-regional comparison of economic structures (either in terms of production, consumption, exports or whatever) or intertemporal comparison of a given economy in terms of structure, one often needs to employ an aggregate index to describe the structural difference (similarity). In this short note, we offer an axiomatic characterization of the measurement of structural difference between economies that gives us a unique difference (similarity) index. 1 ⋆ We are grateful to an anonymous referee and Meng-hun Liu for valuable comments. Correspondence to : Ghuang-Zhen Sun 1 In an interesting study of the measurement of diversity and its value function, Weitzman (1992) starts with the given dissimilarity distance function between any pair of “species”. Solow et al’s