低价卖出、高价买入：肯尼亚市场中的套利与本地价格效应*

中文摘要

本地粮食市场中大幅且规律的季节性价格波动似乎为非洲农民提供了可观的跨期套利机会，但这些机会在很大程度上仍未被利用。通常可以观察到，小规模农户“低价卖出、高价买入”，而非相反。在肯尼亚的一项实地实验中，我们表明，信贷市场不完善限制了农民跨期转移粮食的能力。让农民及时获得信贷，使其能够以较低价格买入、以较高价格卖出，从而增加农场收入，并获得29%的投资回报率。为了理解这些行为变化的一般均衡（GE）效应，我们在不同地点设置了不同的贷款提供密度。我们发现，信贷干预对本地粮食市场的季节性价格波动具有显著影响，并表明这些一般均衡效应影响了个体层面的盈利估计。与现有实验研究的发现不同，我们的结果表明，在本研究所考察的情境中，小额信贷能够提高企业盈利能力，并提示一般均衡效应可能大幅影响小额信贷的有效性。特别是，未考虑这些一般均衡效应，可能导致低估小额信贷干预的社会福利收益。

Abstract

Large and regular seasonal price fluctuations in local grain markets appear to offer African farmers substantial intertemporal arbitrage opportunities, but these opportunities remain largely unexploited. Small-scale farmers are commonly observed to “sell low and buy high,” rather than the reverse. In a field experiment in Kenya, we show that credit market imperfections limit farmers’ abilities to move grain intertemporally. Providing timely access to credit allows farmers to buy at lower prices and sell at higher prices, increasing farm revenues and generating a return on investment of 29%. To understand general equilibrium (GE) effects of these changes in behavior, we vary the density of loan offers across locations. We document significant effects of the credit intervention on seasonal price fluctuations in local grain markets, and show that these GE effects shape individual-level profitability estimates. In contrast to existing experimental work, the results indicate a setting in which microcredit can improve firm profitability, and suggest that GE effects can substantially shape microcredit’s effectiveness. In particular, failure to consider these GE effects could lead to underestimates of the social welfare benefits of microcredit interventions.