英文文献：The Impact of Biofuels Policy on Agribusiness Stock Prices-生物燃料政策对农业企业股价的影响
英文文献作者：Tepe, Fatma Sine,Du, Xiaodong,Hennessy, David A.
英文文献摘要：
Corn markets are important for many industries. These include the seed, fertilizer, meat production/processing and agricultural machinery sectors, all of which are highly concentrated. Oligopoly theory suggests that corn input and field equipment suppliers likely benefit from policies that support corn markets, such as U.S. biofuels policy, while meat companies likely lose. This study investigates the impact of biofuels policy on U.S. agribusiness stock prices. Corn futures prices are found to have a structural change in November 2006, consistent with the expansion of U.S. biofuels policy support. A linear two-factor (S&P500 and corn prices) equilibrium asset pricing model is estimated on two subsamples, one before and one after the estimated change point. Conditional heteroskedasticity in stock returns is accounted for using a GARCH(1,1) model. In the more recent period, corn price increases are found to have positive effects on excess stock returns for seed, fertilizer and machinery companies, while the impact on meat companies is negative. The results may be interpreted as evidence that crop input suppliers gain from U.S. biofuels policies while meat processors lose.

玉米市场对许多行业都很重要。这些部门包括种子、肥料、肉类生产/加工和农业机械部门，所有这些部门都高度集中。寡头垄断理论表明，美国生物燃料政策等支持玉米市场的政策可能会使玉米投入和田间设备供应商受益，而肉类企业则可能会蒙受损失。这项研究调查了生物燃料政策对美国农业企业股票价格的影响。研究发现，2006年11月玉米期货价格发生了结构性变化，这与美国扩大对生物燃料政策的支持相一致。一个线性双因素(标准普尔500和玉米价格)均衡资产定价模型在两个子样本上进行了估计，一个在估计的变化点之前，一个在估计的变化点之后。利用GARCH(1,1)模型来解释股票收益的条件异方差。在最近一段时期，玉米价格上涨被发现对种子、化肥和机械公司的超额库存回报有正面影响，而对肉类公司的影响是负面的。这一结果可以被解释为，作物供应商从美国生物燃料政策中获益，而肉类加工商则损失惨重。