policies revealed through their use as being quantitatively important?<sup>1</sup> How were these TTB policies used and not used during the global economic crisis of 2008‐2009? What is the exporter‐incidence of such imposed policies and how has this changed over time?

In section 2 I first define and construct two new measures of annual, product‐level stocks and flows of imported products subject to these TTBs to address some of the main shortcomings of previous research. First, prior research has typically been unable to construct comprehensive estimates for how much of a country’s imports were subject to TTBs at any point in time. Examining the “stock” of such trade barriers in place over was previously difficult due to the lack of data on both policy removals and the details of which Harmonized System (HS) imported products the new and previously imposed TTBs were affecting. As such, previous work focused almost exclusively on industry‐defined data covering annual counts of the initiation of _new_ investigations and the imposition of _newly imposed_ barriers – “flow” variables that also lacked a normalized (economics‐based) definition for what constituted a “product.” My measures overcome these difficulties through application to new and detailed data drawn from the World Bank’s _Temporary Trade Barriers Database_ . As such, its builds upon prior work documenting the global proliferation of antidumping (AD) use in particular (Prusa, 2001; Zanardi, 2004).

My first result is that there is significant heterogeneity as to the potential economic impact that developed versus developing economy TTB policies have on their trade flows. Most striking is how the divergence between these two groups of policy‐imposing economies is taking place over time.<sup>2</sup> Even before the global economic shock of 2008‐2009, the annual stock of imported products subject to such trade barriers imposed by major emerging economies such as Argentina, Brazil, China, India and Turkey 1 There is also the possibility that such policies are important even despite non‐use (or under‐utilization) – e.g., as an outside option or off‐the‐equilibrium path behavior – if they help facilitate efficiency‐enhancing outcomes. For example, access to (but non‐use of) such policies may serve as insurance for uncertain trade policy negotiators which allow them to take on deeper commitments in a trade agreement than they might otherwise undertake without access to such “exceptions” (Fischer and Prusa, 2003; Hoekman and Kostecki, 2009). I return to this below in the context of one of the questions raised by the pattern of new TTBs resulting from the shock of the global crisis of 2008‐2009.

2 These results relate to recent research (Vandenbussche and Zanardi, 2010; Egger and Nelson, forthcoming) which uses more historical, albeit less‐detailed, data to estimate the aggregate impact of antidumping – the most common of these TTB policies – on trade flows. These two papers use similar gravity model regression approaches and present distinct results: while both find the effect of antidumping on trade flows to be negative, Egger and Nelson conclude that the effect is modest while Vandenbussche and Zanardi interpret the effect as more sizable. A separate approach to estimating the impact of these policies is Gallaway, Blonigen and Flynn (1999), which develop a computable general equilibrium (CGE)‐based approach to estimate the economic welfare impact of the U.S. use of antidumping and countervailing duties on data for 1993.

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