To Pool or Not to Pool : A Closer Look at the Use of Sub-Regressions in Antitrust Class Certification

Did the anticompetitive conduct in question impact all or nearly all class members? This is a question central to a court's class certification decision. To answer this question, a methodology — known as sub-regressions — is being increasingly employed, particularly by defendants' expert witnesses. A key step of a sub-regression type analysis is to partition the data into various subgroups and then to examine data poolability. In this article, I focus on three areas of interest pertaining to sub-regressions. First, I review the related law and economics literature related to this methodology. I then analyze courts' recent class certification decisions in cases where parties introduced sub-regression analysis. I then discuss several methodological challenges, many of which have not been previously acknowledged, and present potential ways to address these challenges. I emphasize that a disciplined and rigorous implementation is crucial for the reliability of sub-regressions