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COPYRIGHT NOTICE: Edited by Richard H. Thaler: Advances in Behavioral Finance, Volume II - page 9 / 23

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BARBERIS AND THALER

the manager can rarely be sure that investors are overvaluing his firm’s shares. If he issues shares, thinking that they are overvalued when in fact they are not, he incurs the costs of deviating from his target capital struc- ture, without getting any benefits in return.

2.3. Evidence

From the theoretical point of view, there is reason to believe that arbitrage is a risky process and therefore that it is only of limited effectiveness. But is there any evidence that arbitrage is limited? In principle, any example of persistent mispricing is immediate evidence of limited arbitrage: if arbitrage were not limited, the mispricing would quickly disappear. The problem is that while many pricing phenomena can be interpreted as deviations from fundamental value, it is only in a few cases that the presence of a mispricing can be established beyond any reasonable doubt. The reason for this is what Fama (1970) dubbed the “joint hypothesis problem.” In order to claim that the price of a security differs from its properly discounted future cash flows, one needs a model of “proper” discounting. Any test of mispric- ing is therefore inevitably a joint test of mispricing and of a model of dis- count rates, making it difficult to provide definitive evidence of inefficiency.

In spite of this difficulty, researchers have uncovered a number of finan- cial market phenomena that are almost certainly mispricings, and persistent ones at that. These examples show that arbitrage is indeed limited, and also serve as interesting illustrations of the risks and costs described earlier.

2.3.1. twin shares

In 1907, Royal Dutch and Shell Transport, at the time completely indepen- dent companies, agreed to merge their interests on a 60:40 basis while re- maining separate entities. Shares of Royal Dutch, which are primarily traded in the United States and in the Netherlands, are a claim to 60 percent of the total cash flow of the two companies, while Shell, which trades primarily in the United Kingdom, is a claim to the remaining 40 percent. If prices equal fundamental value, the market value of Royal Dutch equity should always be 1.5 times the market value of Shell equity. Remarkably, it isn’t.

Figure 1.1, taken from Froot and Dabora’s (1999) analysis of this case, shows the ratio of Royal Dutch equity value to Shell equity value relative to the efficient markets benchmark of 1.5. The picture provides strong evi- dence of a persistent inefficiency. Moreover, the deviations are not small. Royal Dutch is sometimes 35 percent underpriced relative to parity, and sometimes 15 percent overpriced.

This evidence of mispricing is simultaneously evidence of limited arbitrage, and it is not hard to see why arbitrage might be limited in this case. If an ar- bitrageur wanted to exploit this phenomenon—and several hedge funds, Long-Term Capital Management included, did try to—he would buy the

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