Dispersed excess demands, the weak axiom and uniqueness of equilibrium

This paper introduces an economically interpretable hypothesis that implies that mean excess demand satisfies the weak axiom and that competitive equilibrium is unique. The hypothesis requires, roughly, that the consumers' excess demand vectors spread apart on average as their wealth increases. The hypothesis is potentially testable using cross-section data on consumer expenditures and endowments. It is satisfied in a robust class of economies, including those with suitable types of consumer heterogeneity. However, it implies stringent restrictions on the consumers' Engel curves if it is required to hold for every distribution of collinear consumer endowments. (C) 1999 Elsevier Science S.A. All rights reserved.