Comparative Statics and the Gross Substitutes Property of Consumer Demand Anne-Christine Barthel1 and Tarun Sabarwal Abstract. The gross substitutes property of demand is very useful in trying to understand stability of the standard Arrow-Debreu competitive equilibrium. Most attempts to derive this property rely on aspects of the demand curve, and it has been hard to derive this property using assumptions on the primitive utility function. Using new results on the comparative statics of demand in Quah (Econometrica, 2007), we provide simple and easy conditions on utility functions that yield the gross substitutes property. Quah provides conditions on utility functions that yield normal demand. We add an assumption on elasticity of marginal rate of substitution, which combined with Quah's assumptions yields gross substitutes. We apply this assumption to the family of constant elasticity of substitution preferences. Our approach is grounded in the standard comparative statics decomposition of a change in demand due to a change in price into a substitution eect and an income eect. Quah's assumptions are helpful to sign the income eect. Combined with our elasticity assumption, we can sign the overall eect. As a by-product, we also present conditions which yield the gross complements property. PRELIMINARY AND INCOMPLETE 1 Department of Economics, University of Kansas, Lawrence, KS 66045 Email:
[email protected] 1 2 1. Introduction In the standard Arrow-Debreu model, the gross substitutes property of demand provides insight into the question of a competitive equilibrium's stability. Its usefulness in this matter entails the question what assumptions will guarantee this property.