Impact of Income on Price and Income Responses in the Differential Demand System

An extension of the differential demand system model is developed that allows the demand system’s income and price responses to vary with income level. The model’s income flexibility and marginal propensities to consume (MPCs) out of income are made functions of real income measured by the Divisia volume index. The income flexibility is a factor of proportionality underlying all price effects and a change in this term impacts the sensitivity of all demands to prices. Price effects are also made a function of the MPCs using a uniform substitute specification. The model was used to analyze the conditional demands for a group of beverages. The findings indicate that changes in conditional total beverage expenditures result in various income and price elasticity changes across individual beverage products.