卖空机制与食品安全——基于溢出效应的视角

卖空机制通过威慑效应约束厂商的自利动机,为食品安全治理提供了一种可行的资本市场途径。本文利用2015—2018年原国家食品药品监督管理总局披露的食品抽检数据,考察卖空强度对地区食品质量的影响。采用食品类上市公司融券余额在流通市值中占比的加权平均值度量地区卖空强度,体现了食品企业受到的卖空威慑压力。结果发现,卖空强度越大,当地整体的食品抽检质量越好。机制分析发现,卖空威胁在提升上市食品企业产品质量的同时,通过供应链协同、同群效应以及减少信息不对称的途径传导至同地区的其他企业,产生了食品质量治理的溢出效应。异质性分析显示,卖空对食品安全治理的溢出效应在要素市场发育不足、法制相对不健全和欠发达地区更加明显,卖空作为外部监管的补充机制发挥了食品安全治理的功能。因此,完善融资融券制度,适时合理地将食品类上市公司纳入融券标的,为惩治劣质食品提供资本市场手段,对确保食品安全问题“零容忍”具有现实意义。

Spillover Effect of Short Selling on Food Quality: Evidence from China's Food Safety Inspections

Food safety is a great concern not only for human health, but also for social harmony, economic development, and national strength. The Chinese government adopts a double-track approach to enhance food safety: legislation and the continuous improvement of safety supervision. However, with the rapid development of food production technologies and constantly changing business models, food as a category of trust-product has been subjected to ever-increasing information asymmetry, which brings huge challenges for food safety supervision.
The capital market's short-selling mechanism provides a feasible channel for food safety supervision. Short sellers are informed traders with a superior ability to collect and process information. The participation of short sellers in the capital market greatly increases the probability of the discovery of inferior food. Producers of low-quality food may be seriously punished by short sellers through destroyed market value, increased financing costs, customs boycotts, and dismissal of managers. These threats provide a capital market channel to prevent companies from producing inferior food.
The effect of short-selling behavior on food quality does not stop at the short-sold firms, but also has a spillover effect in the form of chain synergy, peer effects, and reduced information asymmetry, which may also increase the overall food quality around the short-sold firms.
We manually collect more than one million food sampling test results provided by the former China Food and Drug Administration from 2015-2018 and examine the impact of food firms' short-selling on the quality of food produced by short-sold target firms in addition to the quality of food produced by the target firms' headquarter regions. We use the annual average of the proportion of short-sold securities to measure a firm's short-selling pressure. If there are multiple food firms from the same regionlisted on the stock market that are subject to short-selling pressure, we use the weighted average proportion of the market value as a measure of the short-selling pressure for the region.
The former China Food and Drug Administration's food safety test results are classified by the sample year and by the regions where the food producers headquartered, but not by the inspecton regions. For each region-year or firm-year, we divide the number of qualified samples by the total number of tests as our proxy for food quality for the underlying region or firm for a given year.
After controlling for a number of region-specific cofactors, including the number of listed firms, legal environment, per capita GDP, quality of human resources, financial constraints in the region, industrialization stage (proxied by industry contributions to total GDP), and technology expenditure in our base model, we find that short selling has a significantly positive effect on regional food quality. Our firm-level regressions also show positive but marginal significant results for short selling on the target firms' food quality. Given the small sample and mostly very high qualification rate, the firm-level results are consistent with our expectations.
A heterogeneity analysis shows that this spillover effect is more prominent in regions with underdeveloped factor markets and relatively weak legal protection, in addition to underdeveloped regions. This result shows that short selling can be used as a supplementary mechanism to formal government supervision to improve food quality.
We address possible endogeneity issues through two approaches: matched comparison and instrumental variables. For the matched comparison, we use 132 region-year observations that are subject to short-selling pressure. We use the proportion of shares held by exchange traded funds (ETFs) for each short-sold food producer as the instrumental variable for short-selling pressure. First, ETFs are mostly tracking funds and their compositions are determined by the weight of certain indexes. Those managers seldom interfere with firm management and thus are exogenous to their firms' behaviors. Second, ETFs provide an important financial supply for short-selling behavior. Thus, the proportion of ETF shares is positively correlated with short-selling pressure. Following these two approaches, we still find a significantly positive effect of short-selling behavior on food quality.
The former possible policy implications of this study show that short selling in the capital markets can act as a governance role to enhance food quality for shorted firms, but also have an important spillover effect that may increase food quality in the firms' surrounding regions. We suggest that the government allows more food firms listed on the stock market can be short.