The Unequal Gains from Product Innovations: Evidence from the U.S. Retail Sector*
中文摘要
本文考察了2004年至2015年间产品创新如何导致美国的通货膨胀不平等。利用零售业的扫描数据，我发现，收入最低的五分位组所面临的零售产品年通货膨胀率比收入最高的五分位组高出0.661个百分点（标准误为0.0535）。将产品种类随时间的变化纳入考量后，这一差异增至每年0.8846个百分点（标准误为0.0739）。在覆盖完整消费篮子的CEX-CPI数据中，年通货膨胀率差异为0.368个百分点（标准误为0.0502）。我考察了以下假说：(i) 由于经济增长和不平等加剧，对高收入家庭所消费产品的相对需求增加；(ii) 企业对此作出回应，推出更多满足此类家庭需求的新产品；(iii) 因此，这些细分市场中持续销售的产品因竞争压力加大而价格下降。利用份额转移（shift-share）研究设计，我发现了因果证据，表明相对需求增加会导致产品种类增加，以及持续销售的产品的通货膨胀率降低。一项校准分析表明，上述假说中的渠道解释了所观察到的通货膨胀不平等的很大一部分（超过50%）。
Abstract
This article examines how product innovations led to inflation inequality in the United States from 2004 to 2015. Using scanner data from the retail sector, I find that annual inflation for retail products was 0.661 (std. err. 0.0535) percentage points higher for the bottom income quintile relative to the top income quintile. When including changes in product variety over time, this difference increases to 0.8846 (std. err. 0.0739) percentage points a year. In CEX-CPI data covering the full consumption basket, the annual inflation difference is 0.368 (std. err. 0.0502) percentage points. I investigate the following hypothesis: (i) the relative demand for products consumed by high-income households increased because of growth and rising inequality; (ii) in response, firms introduced more new products catering to such households; (iii) as a result, the prices of continuing products in these market segments fell due to increased competitive pressure. Using a shift-share research design, I find causal evidence that increasing relative demand leads to increasing product variety and lower inflation for continuing products. A calibration indicates that the hypothesized channel accounts for a large fraction (over 50%) of observed inflation inequality.