信任品市场的竞争效应与传染效应：理论和基于中国食品行业的事件研究

Contagion Effects vs.Competitive Effects in Credence Goods Markets:Theory and Event Study on China's Food Markets

信任品(credence goods)市场的有效运行不仅依赖于同业竞争,也依赖于有效的监管制度和公众对监管制度的信任。特别地,信任品行业中个别企业的丑闻会对其竞争对手企业产生两种相反的效应:在一个监管制度比较弱的市场环境中,会对同行业的竞争对手带来"传染效应",在股票市场上表现为同类企业的股价下降,这反映了市场对监管制度的不信任,严重的情况下会导致相关市场的关闭,造成很大的效率损失;而在一个监管制度比较好的市场环境中,会产生"竞争效应",同行业的竞争对手企业会因此而受益,在股票市场上表现为同类企业股票价格的相对上升,这样可以有效地维护信任品市场的运行。本文发展了一个可以识别信任品市场这两种效应的理论模型和实证方法,并通过事件研究法将其应用于中国的食品行业。本文的实证研究发现,在中国一些主要的信任品市场,传染效应占主导,这表明监管制度的不力和公众对监管制度的不信任是中国信任品行业危机的重要原因。

The well-functioning of credence goods markets hinges on competition and high quality regulation. In particular, seandals by individual firms will produce two opposite effects on their competitors： with weak regulations, it will have contagion effects on their competitors and negatively affect their stock prices, and sometimes even lead to market collapse; with strong regulations, competitive effects will dominate and the competitors will benefit from this and their stock prices will go up, sustaining well-functioning markets. We develop a model and an empirical test to disentangle the two effects and use event study on China＇s food industry to identify the two effects. We find that contagion effects dominate in China in certain major credence goods markets. This may suggest that poor regulatory institutions and people＇s lack of trust in them are important source of the recent crises in China＇s credence goods markets.