Textbook models of demand and supply overlook the potential for market shortages at equilibrium prices and obscure the dependence of demand on income. The use of a step demand function and the delineation of “wants” and “needs” results in different conclusions about the size of market shortages, the role of price in eliminating shortages, and the meaning of normative shortages. The existence of market and normative shortages at equilibrium prices suggests that more attention should be given to optimal rationing of consumer goods when price rationing fails to achieve socially efficient outcomes. This analysis is illustrated using the market for N95 protective masks in the spring of 2020 and includes suggestions for classroom use.

教科书的供需模型忽略了均衡价格下市场短缺的可能性，并掩盖了需求对收入的依赖。阶跃需求函数的使用以及对“需求”和“需求”的描绘得出了关于市场短缺规模，价格在消除短缺中的作用以及规范性短缺的含义的不同结论。均衡价格下市场和规范性短缺的存在表明，当价格配给未能实现社会有效结果时，应更加关注消费品的最优配给。到2020年春季，将使用N95防护口罩市场进行分析，并提供课堂使用建议。