Aggregation Effects on Price and Expenditure Elasticities in a Quadratic Almost Ideal Demand System

While it is well known that demand elasticities calculated at the macro level will in general differ from those calculated at the micro level because of aggregation effects there remain the questions of how large the effects are, and how they vary with the degree of nonuniformity in the income distribution. We explore those questions with models based on a quadratic version of the Almost Ideal Demand System. We investigate the elasticity differences theoretically and then calibrate the models and generate numerical results, using income data for seven countries with widely different distributions. The aggregation effects are found generally to be rather small, even with highly nonuniform income distributions.