568 U.S. 455 (2013)
Amgen Inc. v.
In a Rule 10b-5 securities-fraud class action proceeding under Rule 23(b)(3), must plaintiffs prove the materiality of alleged misstatements at the class certification stage to establish predominance, and may defendants defeat class certification by presenting evidence that the alleged misstatements were immaterial?
Under Rule 23(b)(3), a class may be maintained if common questions of law or fact predominate over any questions affecting only individual members. In securities-fraud actions under Section 10(b) and Rule 10b-5, plaintiffs may invoke Basic Inc. v. Levinson's fraud-on-the-market presumption of reliance by showing that the alleged misstatements were public, that the security traded in an efficient market, and that the plaintiffs traded the security between the time of the misstatements and the corrective disclosures. Materiality is an element of a Rule 10b-5 claim assessed under an objective standard and is common to the class; it need not be proven at class certification to satisfy Rule 23(b)(3), and defendants may not defeat certification at that stage by introducing immateriality evidence because materiality either will be resolved commonly for the class or will defeat the claim for all class members together.
No. Securities-fraud plaintiffs need not prove materiality at the class certification stage to obtain the fraud-on-the-market presumption and satisfy Rule 23(b)(3)'s predominance requirement, and defendants may not defeat certification by offering immateriality evidence at that stage. The Supreme Court affirmed the Ninth Circuit's judgment.
Amgen is a pivotal class certification case. It lowers the certification threshold for Rule 10b-5 class actions by confirming that plaintiffs need not prove materiality to show predominance, thereby preventing defendants from using immateriality evidence to block certification. The decision preserves the efficiency of class proceedings by ensuring that truly common merits issues are decided later, all at once, for everyone. After Amgen, plaintiffs still must establish the Basic predicates of public statements, market efficiency, and trading during the relevant period, but not materiality, at certification. Subsequent Supreme Court decisions refined, but did not displace, Amgen. In Halliburton II (2014), the Court allowed defendants at class certification to rebut the Basic presumption by showing no price impact, which is distinct from materiality. Thus, the current landscape is: plaintiffs need not prove materiality at certification; defendants cannot defeat certification with immateriality evidence; but defendants may use price-impact evidence to rebut the presumption at certification.