Vyacheslav Fos is Assistant Professor of Finance at Boston College. This post is based on an article by Professor Fos and Pierre Collin-Dufresne, Professor of Finance at the Swiss Finance Institute. Related research from the Program on Corporate Governance includes Pre-Disclosure Accumulations by Activist Investors: Evidence and Policy by Lucian Bebchuk, Alon Brav, Robert J. Jackson Jr., and Wei Jiang; and The Law and Economics of Blockholder Disclosure by Lucian Bebchuk and Robert J. Jackson Jr. (discussed on the Forum here).
In our paper, Do Prices Reveal the Presence of Informed Trading?, forthcoming in the Journal of Finance, we study how empirical measures of stock illiquidity and of adverse selection respond to informed trading by activist shareholders.
An extensive body of theory suggests that stock illiquidity, as measured by the bid-ask spread and by the price impact of trades, should be increasing in the information asymmetry between market participants. An extensive empirical literature employing these illiquidity measures thus assumes that they capture information asymmetry. But, do these empirical measures of adverse selection actually increase with information asymmetry? To test this question one would ideally separate informed from uninformed trades ex-ante and measure their relative impact on price changes. However, since we generally do not know the traders’ information sets, this is hard to do in practice.
