... their private information had been unsuccessful. Insiders did gain increased profitability when they exploited this private information (Seyhun, N 1992). On top of this he also showed that in the late 1980s, top-level insiders earned abnormal returns of approximately 9%, and this was during the year following open-market purchases and sales. Thus, he shows that an insider facing firm-level restrictions on insider trading faces the loss of significant profits that could otherwise be earned, even in a legal environment attempting to restrict trading profits, therefore the legislation does not work, and insider trading continues to produce higher returns. This evidence discredits the theory that all market participants receive and act on all of the relevant information as soon as it becomes available, since insider's can profit from insider information, therefore I would conclude that the market itself is not of strong form, as Seyhun states. The semi-strong form of EMH ascertains that ...

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