First, complainant countries may face different costs to litigate otherwise identical cases. For example, introduction of the Advisory Centre on WTO Law (ACWL) in 2001 has established at least a two-tiered cost structure for potential litigants – low-income country users of the ACWL receive highly subsidized legal services to which non-users of the ACWL do not have access.<sup>18</sup> Second, the government’s objective function used to decide whether to challenge any potential WTO violation may be more complex than that implied by this simple one time, social-welfare maximizing cost-benefit framework. Governments may also be motivated by domestic politics and place a higher weight on the benefits arising to particular domestic firms with trade dispute interests relative to its costs (Davis, 2012). Alternatively, even national-welfare maximizing governments may pursue disputes in which the economic costs exceed the industry-level benefits if the expected outcome arising from that dispute has significant positive externalities. For example, potential externalities may include precedent-setting (Pelc, forthcoming), especially if this model is reformulated as a repeated game.<sup>19</sup> Third, the set of potential violations for countries to choose between when deciding which disputes to initiate may not be unbiased. Maggi and Staiger (2011), for example, provide a theory that motivates selection bias as arising endogenously based on dispute settlement rulings. Furthermore, Bown (2002, 2004a) motivates selection bias as resulting from countries being more likely to violate rules by imposing policies ex ante against trading partners with limited trade retaliation capacity, given that retaliation is the ultimate enforcement remedy in WTO dispute settlement.

Our final thought experiment for this section is to use these market access data to provide a rough estimate of the economic importance of the total trade at stake in these disputed products. For the 308 cases initiated between 1995 and 2011, the aggregate annual value of (pre-dispute) respondent imports in disputed products was $937.5 billion, or an average of more than $55 billion per year. Put differently, this

> 18 Between its inception in 2001 and 2011, the ACWL provided the legal services on behalf of either a complainant or respondent in more than 35 WTO disputes, or almost 20 percent of all disputes filed during that period. If the ACWL itself were a WTO member country, it would be the third most frequent litigant during the period trailing only the US and EU and ahead of China.  Bown and McCulloch (2010) provide an empirical exploration into a number of different margins along which the introduction of the ACWL into WTO dispute settlement may be affecting the pattern of the subsequent caseload. Busch, Reinhardt, and Shaffer (2009) provide a broader review of the WTO legal capacity concerns of low-income countries.

> 19 Alternatively, an interpretation of the simultaneous Boeing-Airbus disputes is that they were part of a prisoner’s dilemma-like subsidy-setting game, whereby the US and EU used dispute settlement as an attempt to coordinate (or self-enforce) a reciprocal reduction of subsidies.

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