Insider Trading in the Market with Rational Expected Price

Abstract

Kyle (1985) builds a pioneering and influential model, in which an insider with long-lived private information submits an optimal order in each period given the market maker's pricing rule. An inconsistency exists to some extent in the sense that the ``constant pricing rule " actually assumes an adaptive expected price with pricing rule given before insider making the decision, and the ``market efficiency" condition, however, assumes a rational expected price and implies that the pricing rule can be influenced by insider's strategy. We loosen the ``constant pricing rule " assumption by taking into account sufficiently the insider's strategy has on pricing rule. According to the characteristic of the conditional expectation of the informed profits, three different models vary with insider's attitudes regarding to risk are presented. Compared to Kyle (1985), the risk-averse insider in Model 1 can obtain larger guaranteed profits, the risk-neutral insider in Model 2 can obtain a larger ex ante expectation of total profits across all periods and the risk-seeking insider in Model 3 can obtain larger risky profits. Moreover, the limit behaviors of the three models when trading frequency approaches infinity are given, showing that Model 1 acquires a strong-form efficiency, Model 2 acquires the Kyle's (1985) continuous equilibrium, and Model 3 acquires an equilibrium with information released at an increasing speed.