Hierarchic Demand and the Engel Curve for Variety
提出层级需求系统，其中消费者只购买部分商品，并用层级线性支出系统展示其性质。实证表明，购买的商品数量随总支出增加而扩大，强调角点解和购买决策在需求研究中的重要性。
Ahstract-The usual treatment of consumer demand theory assumes a solution to the demand equations with positive quantities of all commodities. This paper characterises a class called hierarchic demand systems for which only a subset of commodities are in the purchased set. The hierarchic linear expenditure svstem is used to illustrate interesting properties of such systems. The empirical section shows how the number of commodities purchased expands with total expenditure both in aggregate and for commodity groups. The data clearly establish the empirical importance of corner solutions and of the purchase decision in demand studies.