This paper uses unique Spanish panel data on household expenditures to test whether unobservable heterogeneity in household demands (taste, etc.) is correlated with total expenditures (income). The main finding is that tastes are indeed correlated with income for about half of the goods considered, implying that cross-sectional estimates of income elasticities for these goods are biased. The goods are the following: food eaten outside home, alcohol and tobacco, transportation, and energy. The elasticity of alcohol and tobacco is more than halved when taking unobserved heterogeneity into account. For transportation, the bias is sufficiently large to misclassify the good as a luxury.

Inspired by the recent literature on aggregation theory, this paper introduces HITS, a semiparametric model of consumer demand that allows for diversity in tastes. The strong variation of budget shares observed across income strata can arise from two economic factors: the individual income effect, and taste differences between poor and rich households. Consumer expenditure surveys that report repeated cross-sections do not permit the direct measurement of these two effects, and the paper solves this difficulty by developing a new microeconometric framework. We model consumer demand by a class of Nearly Ideal Demand Systems parameterized by a unique taste parameter. Linear heterogeneity allows GMM estimation of the structural coefficients on an aggregate time series, and the joint density of spending and tastes is recovered from cross-sections by a nonparametric procedure involving a deconvolution. We develop an asymptotic theory and demonstrate the accuracy of the algorithm by Monte Carlo and bootstrap simulations. The model is estimated on four size groups using the British Family Expenditure Survey (1968-98). We report a strong correlation between income and tastes, which explains most of the observed variation of budget shares with income. Unlike some earlier models, this new approach is consistent with both the yearly cross-sections of individual choices and the dynamics of aggregate shares.

This dissertation studies the effect of heterogeneity in consumer incomes on outcomes in vertically differentiated markets. When products are differentiated in quality, the consumer's choice of a particular product is a function of her income. Thus, the distribution of incomes plays an important role in shaping the demand for individual products in vertically differentiated markets. The first two chapters of the dissertation study the demand for passenger cars and trucks in the US. These vehicles are differentiated by quality that depends on vehicle's age. The first chapter studies the relationship between the distribution of consumer incomes and the distribution of vehicle vintages using a dynamic, heterogeneous agents model. The model predicts that higher per capita incomes are associated with younger vehicle stocks, if the vehicle ownership rates are high. If the per capita incomes are low, and so are the endogenous vehicle ownership rates, increases in income may lead to the aging of vehicles, by encouraging entry of lower income consumers into vehicle ownership via purchases of older vehicles. Higher levels of income inequality are associated with older vehicle stocks. The second chapter of the dissertation asks whether some of the observed increases in the average age of vehicles in the US can be attributed to the rise in real consumer incomes and the resulting changes in the composition of demand for different vehicle vintages. The dynamic, non-stationary, heterogeneous agents model, estimated on the aggregate vehicle ownership data for the US over the 1967-2001 period, provides a positive answer to this question. The third chapter of the dissertation studies the effect of inequality in consumer incomes on firms' entry, location, and pricing decisions in a static oligopoly model of vertically differentiated products. This paper computes the Nash equilibrium of a three-stage game similar to Shaked and Sutton (1982), to find that greater inequality in consumer incomes leads to the entry of more firms and results in more intense quality competition among the entrants. The consumption inequality is lower and the aggregate consumer welfare is higher in economies with greater income inequality.

In this dissertation, we show how the firm can improve its revenue and competitiveness through segmenting the market by exploring consumer heterogeneity. In the first essay, we show that asymmetric assortment breadth among two competing retailers can emerge as an equilibrium when consumers differ in their prior knowledge about their product preferences and their shopping costs. Under this equilibrium, the full line retailer expands the market demand by attracting the uninformed consumers with large shopping costs and the single product retailer passes on the savings from a streamlined assortment to the informed consumers by setting a lower price. Therefore, the two retailers soften the competition between them and both achieve higher profits. In the second essay, we consider a setting in which consumers experience distinct instances of need for a durable product at random intervals and derive random amount of utility from each instance. Consumers are differentiated according to the frequency with which they experience instances of need. For a firm that provides a durable product to such a market, we consider the implications of selling versus renting on a per-usage basis. Selling minimizes transaction costs, but may result in inefficient utilization of units that are produced. Alternatively, per-usage rentals allow more utility to be generated per unit of product that is produced. Focusing on these trade-offs, we identify conditions under which the firm should sell, offer per-usage rentals, or offer a combination of the two. In the third essay, we continue to use the durable good framework to study how various forms of government subsidy programs shift consumer's demand patterns and thus generate different magnitude of additional savings in resource consumption. We give the conditions under which each type of cash rebate programs does the best in generating resource savings per dollar spent.

Demographic differences, like young and elderly, and healthy and disabled, are summarized as consumers' heterogeneity in expenditure shares, and introduced into an otherwise standard HO model, together with income distribution in this paper. We prove that free trade may hurt consumers who spend more on the exporting good if the volume of trade is small, while redistributing more income to consumers who spend more on the exporting good may make everyone in the country better off. By contrast, redistributing more income to consumers who spend more on the importing good may make everyone in the country worse off.

This paper studies identification and estimation of a dynamic discrete choice model of demand for differentiated product using consumer-level panel data with few purchase events per consumer (i.e., short panel). Consumers are forward-looking and their preferences incorporate two sources of dynamics: last choice dependence due to habits and switching costs, and duration dependence due to inventory, depreciation, or learning. A key distinguishing feature of the model is that consumer unobserved heterogeneity has a Fixed Effects (FE) structure -- that is, its probability distribution conditional on the initial values of endogenous state variables is unrestricted. I apply and extend recent results to establish the identification of all the structural parameters as long as the dataset includes four or more purchase events per household. The parameters can be estimated using a sufficient statistic - conditional maximum likelihood (CML) method. An attractive feature of CML in this model is that the sufficient statistic controls for the forward-looking value of the consumer's decision problem such that the method does not require solving dynamic programming problems or calculating expected present values.