中文摘要
联合国2015年可持续发展目标的第一项是：“在全世界消除一切形式的贫困。”这一宽泛目标意味着存在一系列贫困线，由此引出了全球贫困线适当下限与上限的问题。“每日一美元”贫困线（按通货膨胀调整后，以2017年购买力平价计为P$2.15）被广泛接受为全球贫困线下限（GLBPL）。然而，尽管不同国家、组织和作者采用了更高的贫困线，但对于全球贫困线上限（GUBPL）尚无共识。我们采用两种概念上不同的方法估计GUBPL，这两种方法均立足于贫困测度的聚焦公理与标准经济学社会福利测度之间的张力。我们将候选GUBPL设定为以下两者之一：(i) 与实现适足物质福祉相一致的消费水平；或 (ii) 边际效用“足够接近”零时的消费水平。无论采用哪种方法，基于一系列福祉测度的实证结果均表明，包括世界银行报告的最高贫困线P$6.85在内的临时设定贫困线，都远低于可作为GUBPL合理候选值的水平。将这两种方法应用于四项不同的福祉指标，所有实证结果均表明，GUBPL至少应为P$21.5，是标准GLBPL P$2.15的十倍。同时采用全球贫困线下限和上限，可在两种同样极端的标准之间取得平衡：一方面，“每日一美元”标准具有极强的排他性，将物质福祉水平很低、因而收入边际效用很高的人群归为“非贫困”；另一方面，GUBPL具有同样极强的包容性，仅将物质成就处于全球较高水平且收入边际效用较低的人群归为“非贫困”。
Abstract
The first of the United Nations 2015 Sustainable Development Goals is: “End poverty in all its forms everywhere.” An implication of this broad goal is the existence of an array of poverty lines, which raises the question of an appropriate lower-bound and an upper-bound to global poverty lines. The ‘dollar-a-day’ poverty line (updated for inflation to P$2.15 in 2017 PPP) is widely accepted as a global lower-bound poverty line (GLBPL). However, while different countries, organizations, and authors use higher poverty lines, there is no consensus on a global upper bound poverty line (GUBPL). We estimate a GUBPL using two conceptually distinct approaches, both grounded in the tension between the focus axiom for poverty measures and standard economic social welfare measures. We set a candidate GUBPL either at: (i) the consumption consistent with the achievement of adequate material well-being or (ii) the consumption level where marginal utility is “near enough” zero. Using either approach, empirical results across an array of measures of well-being demonstrate that ad hoc poverty lines, including the World Bank's highest reported poverty line of P$6.85, are far too low to be plausible candidates for a GUBPL. Using the two approaches across four distinct indicators of well-being all of the empirical results suggest a GUBPL of at least P$21.5, ten times higher than the standard GLPBL of P$2.15. The use of both a lower bound and upper bound global poverty line balances the radically exclusive nature of the ‘dollar-a-day’ standard, which classifies people with very low levels of material well-being and hence very high marginal utility of income as “not poor” with an equally radically inclusive GUBPL which counts only those with globally high material achievement and low (ish) marginal utility of income as “not poor.”