Collaborative Research: Differentiated Product Oligopolies and the Antitrust Litigation Model

美国反垄断当局越来越多地根据拟议的合并如何影响特定寡头垄断模式的战略形势来评估横向合并。 最突出的是对产品有差异的市场中的横向合并的分析。 在这种情况下，司法部工作人员开发了一种反托拉斯诉讼模式，模拟合并，作为一种筛选手段，以帮助确定何时可能出现竞争问题。司法部工作人员使用资产负债管理分两步评估合并的影响。 首先，工作人员收集价格和市场份额数据，并估计一些需求参数。 其次，将这些数据插入模型，以生成估算成本参数和合并后预测。 尽管ALM的预测很方便，但对这种方法的有用性至关重要的一些问题仍然没有答案。 首先，在特定模型假设下产生的价格预测与更一般的自然发生情况下的结果之间的关系尚不清楚。 第二，即使在理论领域，驱动预测的单边效应的动机也是微妙的，可能没有什么解释力。 第三，该模型用于区分市场结果中相对细微的差异。 因此，关于兼并前需求参数估计的潜在准确性的一些信息将是有用的。 实验室方法为研究这些重要问题提供了理想的媒介。 在实验室中，需求系统、战略互动的性质和潜在的均衡预测可以被先验地指定。 因此，预测和结果之间的关系可以明确地检查。 该提案描述了三个实验，旨在提供一些见解的重要性，假设的ALM。 首先，假设一个模型的潜在需求系统是logit，并且卖方是Bertrand竞争者，这是ALM的假设。 在这些“最佳机会”情况下进行的实验可以评估实际价格和预测价格与市场份额之间的相关性，以及模型估算成本措施的准确性。 此外，分析合并后的业绩将允许检查的能力，理论上的比较静态影响，以预测行为的结果 第二，虽然logit需求系统提供了分析的优势，没有先验的理由相信，许多自然的需求系统是logit的。 一个实验将检查潜在需求系统变化的影响。 从相同的可观察到的合并前的信息，我们可以评估的重要性的基本需求规格的前和合并后的性能转移的需求系统从logit的线性。 第三个实验评估的重要性，假设卖方是伯特兰（数量设置）的竞争对手。 尽管经济学家通常假设，当产品差异化时，战略互动是伯特兰的，但没有充分的理由认为这一假设反映了自然环境中竞争的本质。 保持可观察的市场信息不变，我们可以评估关于战略互动性质的假设的重要性。

Increasingly, U.S. antitrust authorities evaluate horizontal mergers in terms of how proposed consolidations may affect the strategic situation in specific oligopoly models. Most prominent is the analysis of horizontal mergers in markets where products are differentiated. In such contexts Department of Justice (DOJ) staff have developed an Antitrust Litigation Model (ALM) merger simulation as a screening device to help determine when competitive problems might arise. The DOJ staff use the ALM to assess the effects of a merger in a two step process. First, staff collect price and market share data, and estimate some demand parameters. Second, these data are inserted into the model to generate imputed cost parameters and post-merger predictions. Despite the convenience of the ALM's predictions, a number of questions critical to the usefulness of this approach remain unanswered. First, the relationship between price predictions generated under model-specific assumptions and outcomes in more general naturally occurring circumstances is not clear. Second, even on the domain of the theory, the incentives that drive predicted unilateral effects are subtle and may have little explanatory power. Third, the model is used to distinguish between relatively subtle differences in market outcomes. Some information about the potential accuracy of pre-merger demand parameter estimates would thus be useful. Laboratory methods provide an ideal medium for examining these important questions. In the laboratory the demand system, the nature of strategic interactions and the underlying equilibrium predictions can be specified a priori. Thus, the relationship between predictions and outcomes can be examined explicitly. This proposal describes three experiments designed to provide some insight into the importance of the assumptions underlying the ALM. First, suppose that the underlying demand system for a model is logit and that sellers are Bertrand competitors, the assumptions of the ALM. An experiment conducted under these "best shot" circumstances could evaluate the correlation between actual and predicted prices and market shares, as well as the accuracy of the models' imputed cost measures. Further, analysis of post-merger performance would allow examination of the capacity of theoretical comparative statics effects to predict behavioral outcomes Second, although a logit demand system offers analytic advantages, there is no a priori reason to believe that many natural demand systems are logit. An experiment would examine the effects of the changes in the underlying demand system. Starting with identical observable pre-merger information, we can evaluate the importance of the underlying demand specification on pre- and post-merger performance by shifting the demand system from logit to linear. A third experiment assesses the importance of assuming that sellers are Bertrand (quantity-setting) competitors. Although economists typically assume that strategic interactions are Bertrand when products are differentiated, there is no good reason for supposing that this assumption reflects the nature of competition in natural contexts. Holding the observable market information fixed, we can evaluate the importance of an assumption about the nature of strategic interactions.