谁在驱动不平等？

中文摘要

哪些国家驱动了全球不平等？哪些州驱动了美国不平等？我们刻画了一类能够回答这些问题的收入不平等测度，此类测度既允许按子群进行加性分解，又允许分解为组内与组间成分的乘性分解。其核心测度就是两个随机抽取个体之间收入的期望比率。我们表明，自1990年以来全球不平等有所下降，其驱动因素是国家间差距的缩小。不平等主要由大型中等收入国家（印度、中国）和贫困国家（刚果民主共和国、埃塞俄比亚）驱动。在美国，不平等加剧可由各州内部差距的扩大来解释，而州间不平等则依然有限。

Abstract

Which countries drive global inequality? Which states drive US inequality? We characterize the class of inequality measures that can answer these questions, permitting both an additive decomposition by subgroup and a multiplicative decomposition into within- and between-group components. Its central measure is simply the expected ratio of incomes between two randomly selected individuals. We show that global inequality fell since 1990, driven by declining disparities between countries. Inequality is primarily driven by large middle-income countries (India, China) and poor countries (Democratic Republic of Congo, Ethiopia). In the US, rising inequality is explained by widening gaps within states, while between-state inequality remains limited.