William & Mary Law Review


Plaintiffs commonly bring two distinct types of claims under section 10(b) of the Securities Exchange Act of 1934: (1) claims of material misrepresentations or omissions, and (2) claims of tradebased market manipulation. Despite the distinctive features of the two types of claims, courts have tended to treat them identically when applying the “fraud on the market” doctrine. In particular, courts have required both types of plaintiffs to make identical showings that the relevant security was traded in an “efficient market” in order to gain a presumption of reliance. The reasons for requiring such a showing by plaintiffs in a misrepresentation case are, however, inapplicable in market manipulation cases. Plaintiffs alleging market manipulation should not be required to demonstrate an efficient market in order to benefit from the fraud on the market doctrine’s presumption of reliance. If plaintiffs are made to make any showing at all, it should be a showing of loss causation.