We propose and estimate a model of endogenous informed trading that is a hybrid of the PIN and Kyle models. When an informed trader trades optimally, both returns and order flows are needed to identify information asymmetry parameters. Empirical relationships between parameter estimates and price impacts and between parameter estimates and stochastic volatility are consistent with theory. We illustrate how the estimates can be used to detect information events in the time series and to characterize the information content of prices in the cross-section. We also compare the estimates to those from other models on various criteria. Received April 5, 2017; editorial decision September 21, 2017 by Editor Itay Goldstein.

In an “activist risk arbitrage,” a shareholder attempts to improve terms of an announced M&A through public campaigns. Activists target deals with low premiums and those susceptible to managerial conflicts of interest, including going‐private deals and deals in which CEOs receive outsized payments. Activist arbitrageurs are associated with a significant decrease in the probability that targets will be sold to the announced bidders, and an increase in the premium paid, both ex post among surviving deals and ex ante among all deals. Activist arbitrage serves as a governance mechanism in M&A and earns higher returns than passive arbitrage.

We analyze dynamic trading by an activist investor who can expend costly effort to affect firm value. We obtain the equilibrium in closed form for a general activism technology, including both binary and continuous outcomes. Variation in parameters can produce either positive or negative relations between market liquidity and economic efficiency, depending on the activism technology and model parameters. Two results that contrast with the previous literature are that (a) the relationship between market liquidity and economic efficiency is independent of the activist's initial stake for a broad set of activism technologies, and (b) an increase in noise trading can reduce market liquidity because it increases uncertainty about the activist's trades (the activist trades in the opposite direction of noise traders) and thereby increases information asymmetry about the activist's intentions.