The third category of "available information" was that to which only certain groups, such as corporate insiders, were privy. If this kind of information was always reflected in prices, and insiders could not make excess profits on the basis of it, a market was "strong form" efficient. "We would not, of course, expect this [strong form] model to be an exact description of reality," wrote Fama (1970, p. 409), and indeed there was already evidence against it.

Donald MacKenzie, An Engine, Not a Camera, loc. 295