A key question in class certification decisions in the United States is whether class-wide evidence can be used to determine whether the challenged conduct resulted in harm to all or almost all proposed class members. One popular approach, which the plaintiffs’ experts sometimes call the “in-sample prediction approach,” claims to estimate the impact of the challenged conduct on each transaction. In a price fixing class action, the in-sample prediction approach purports to provide an estimate of the overcharge on each transaction, which we refer to as a transaction-specific overcharge.
In “Evaluating the Alleged Misconceptions about the In-Sample Prediction Approach to Assessing Common Impact,” Celeste Saravia and Daniel Ramsey author a response to a previous article about this two-step econometric method for establishing common impact. In that previous article, the authors claimed that critiques of the approach’s reliability rest on three misconceptions about the approach. In this article, Dr. Saravia and Dr. Ramsey explain that the approach is unreliable because it fails two fundamental tests of reliable econometric methods and is contradicted by the academic literature.
This article was originally published by Antitrust Magazine in August 2026.
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