发表机构
Emory University; Research Institute for Economics and Business Administration, Kobe University（埃默里大学; 神户大学经济经营研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文在含随机因素的有限期最优储蓄问题中，刻画了条件不耐性下消费呈凹性的充要条件，指出无该条件时HARA效用是均匀凹性的充要条件，并通过示例说明违反条件的影响。
AI 中文摘要
凹性消费函数意味着边际消费倾向随财富增加而下降。本文在具有随机贴现、收益、收入及借贷约束的有限期最优储蓄问题中，刻画了能保证该性质的效用函数。在条件不耐性（条件期望贴现毛回报率不超过1）下，消费始终为凹的当且仅当绝对谨慎度的倒数$-u''/u'''$为凹函数；无此条件时，双曲绝对风险厌恶（HARA）是均匀凹性的充要条件。一个确定性单期示例表明，违反条件不耐性会使非HARA效用对应的消费呈严格凸性。
英文摘要
Concave consumption functions imply a marginal propensity to consume that falls with wealth. I characterize the utility functions that guarantee this property in finite-horizon optimal saving problems with stochastic discounting, returns, income, and borrowing limits. Under conditional impatience---the conditional expected discounted gross return does not exceed one---consumption functions are always concave if and only if inverse absolute prudence, $-u''/u'''$, is concave. When no conditional-impatience restriction is imposed, hyperbolic absolute risk aversion (HARA) is necessary and sufficient for uniform concavity. Thus conditional impatience permits declining marginal propensities to consume for a preference class strictly larger than HARA.
