On 25 July 2015, the United States District Court for the Northern District of Texas issued the much-anticipated ruling on class certification in Erica P. John Fund, Inc. v. Halliburton Co. The economic analysis of price impact was front and center in the Court’s ruling. Halliburton, supported by the expert analysis of NERA Senior Vice President Lucy P. Allen, demonstrated to the Court that there was no price impact stemming from five of the six alleged corrective disclosures by using economic principles that generally apply to securities class action cases, as well as complex statistical analyses that may apply to certain cases. This paper, by NERA Senior Consultant Jorge Baez and former Senior Consultant Dr. Renzo Comolli, examines the economic and statistical principles used in Ms. Allen’s analysis, as well as how the decision underscores the necessity of sound economic analysis for class certification.