In this securities fraud case, U.S District Judge Deborah Batts denied class certification for AIG bonds and sharply limited the remainder of plaintiffs’ case due to the failure of plaintiffs and their expert to demonstrate loss causation. Moreover, Judge Batts rejected plaintiffs’ claim that 10% is the generally accepted level in financial economics for event study statistical significance. Compass Lexecon expert Charles Cox testified on behalf of AIG that the economic evidence did not establish market efficiency for AIG bond markets and rebutted the testimony of plaintiffs’ expert on market efficiency, statistical significance, loss causation, and economic methodology. Judge Batts cited Dr. Cox’s testimony favorably in her opinion. Dr. Cox was supported by Laurel Van Allen in Compass Lexecon’s Chicago office. We worked with Daniel J. Leffell and Daniel J. Kramer of Paul, Weiss, Rifkind, Wharton & Garrison LLP.