The skill premium and inequality, more generally, have increased dramatically in the United States since 1980; see the top panel of figure 1. This rise has coincided with a substantial increase in the relative supply of skilled workers; see the bottom panel of figure 1. To the extent that relative supply and demand shape relative prices, these patterns reveal a sizable skill-biased shift in relative demand. A large literature across a range of subfields within economics investigates the roles of various economic forces in generating such a shift. This literature emphasizes in particular two broad categories of observable shocks: a fall in the quality-adjusted cost of capital equipment that is relatively more substitutable for less skilled labor (including computers, software, industrial robots, etc.) and demand shocks biased toward jobs that are relatively intensive in skilled labor (induced by international trade, offshoring, structural transformation, etc.). One central goal of this broad literature is to quantify how important each shock is in explaining the evolution of the skill premium andhowmuch remains unexplained (often referred to as “skill-biased technological change”). “Trading Up and the Skill Premium” does a good job of empirically motivating the potential importance of a particular channel that has not featured prominently (or at all) in this literature: a within-industry version of the link between structural transformation and inequality. The authors provide evidence that higher-income consumers disproportionately purchase higher-quality varieties within industries and that higher-quality varieties within industries are skill intensive. This evidence suggests that an increase in incomewill generate a skill-biased demand shock (i.e., an increase in relative expenditure on skill-intensive varieties at fixed prices) within industries. Themain point of our discussion is that this first pass at quantification is missing two key elements. First, the connection between the model

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更普遍地说，美国的技能溢价和不平等自 1980 年以来急剧增加；参见图 1 的顶部面板。这种增长与技术工人的相对供应量的大幅增加相吻合；参见图 1 的底部面板。就相对供给和需求影响相对价格而言，这些模式揭示了相对需求的相当大的技能偏向转变。经济学中一系列子领域的大量文献调查了各种经济力量在产生这种转变中的作用。这些文献特别强调了两大类可观察到的冲击：资本设备的质量调整成本下降，相对更可替代技能较低的劳动力（包括计算机、软件、工业机器人等）。）和需求冲击偏向于技术劳动力相对密集的工作（由国际贸易、离岸外包、结构转型等引起）。这一广泛文献的一个中心目标是量化每次冲击在解释技能溢价演变方面的重要性，以及有多少仍未得到解释（通常称为“偏向技能的技术变革”）。“向上交易和技能溢价”在实证上很好地激发了在该文献中没有突出（或根本没有）突出显示的特定渠道的潜在重要性：结构转型与不平等之间联系的行业内版本。作者提供的证据表明，高收入消费者不成比例地购买行业内的优质品种，而行业内的优质品种是技能密集型的。这一证据表明，收入的增加将在行业内产生偏向于技能的需求冲击（即以固定价格购买技能密集型品种的相对支出增加）。我们讨论的要点是，量化的第一遍缺少两个关键要素。一、模型之间的连接