Defensive Tactics and Optimal Search: A Simulation Approach

57 Pages Posted: 7 Jul 2016 Last revised: 24 Sep 2016

See all articles by Ronald J. Gilson

Ronald J. Gilson

Stanford Law School; Columbia Law School; European Corporate Governance Institute (ECGI); Stanford Law School

Alan Schwartz

Yale Law School

Multiple version iconThere are 2 versions of this paper

Date Written: July 6, 2016


The appropriate division of authority between a company’s board and its shareholders has been the central issue in the corporate governance debate for decades. This issue presents most vividly for defensive tactics: the extent to which the board of a potential acquisition target is allowed to prevent the shareholders from responding directly to a hostile bid. In the US today, the board’s power is extensive; control largely lies with the board. Normative evaluations of current law face two obstacles. First, defensive tactics raise the social welfare question whether, or to what extent, these tactics deter ex ante efficient takeovers. This question cannot be answered empirically because the econometrician can observe bids but cannot observe deterred bids. The social welfare issue is also difficult to resolve using current analytical techniques because the market for corporate control is unusually complex: in it, financial and strategic buyers search for mismanaged companies or synergy targets; and some synergy targets search for acquirers. Turning to targets, the question which defensive tactics level maximizes shareholder welfare also is difficult to answer because of the qualitative nature of defensive tactics: Is a poison pill more or less privately efficient than a staggered board? What are the welfare consequences of combining a pill with a staggered board or a supermajority voting requirement? In this paper, we write a search equilibrium model of the market for corporate control and solve it by simulating plausible parameters for the variables of interest. Because we specify the number of ex ante efficient acquisitions that could be made, we can estimate market efficiency – the ratio of made matches to good matches – under legal regimes that are more or less friendly to defensive tactics. Also, we argue that the common metric among defensive tactics is time: the ability of various tactics to delay bid completion and thus reduce bidder, and thereby increase target, returns.

We have two important results: First, strong defensive tactics reduce market efficiency significantly. Our simulations suggest that approximately a $100 billion in deal value is lost each year in consequence of these tactics. Simulations are only suggestive and our simulated model likely overstates the welfare loss. Nevertheless, the result that defensive tactics cause economically significant welfare losses would stand even if our magnitude estimate is halved. Second, the defensive tactics level that maximizes target shareholder welfare is materially higher than the level that maximizes social welfare. These results also support a methodological claim: equilibrium analysis can illuminate regulatory issues regarding the market for corporate control.

Keywords: corprorate acquisitions, defensive tactics, search theory, simulation

JEL Classification: C63, D23, G18, G34, G38, K22

Suggested Citation

Gilson, Ronald J. and Schwartz, Alan, Defensive Tactics and Optimal Search: A Simulation Approach (July 6, 2016). European Corporate Governance Institute (ECGI) - Finance Working Paper No. 472/2016, Stanford Law and Economics Olin Working Paper No. 495, Yale Law & Economics Research Paper No. 552, Available at SSRN: or

Ronald J. Gilson

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