(HS-06) product level from 1988:Q1-2010:Q4.<sup>9</sup> Specifically, our dependent variable is the count of HS06 imported products on which the government of economy _j_ conducts a _new_ temporary trade barrier investigation against trading partner _i_ in quarter _t_ and against which there is not already an existing TTB in place.<sup>10</sup> Inclusion of all forms of temporary import restrictions is important because more recent episodes of import protection – including the 2001-3 global safeguard on steel products imposed by the US, EU, and a number of other countries, and the 2009 China-specific safeguard the US imposed on imports of tires – took place under these alternative temporary trade barrier policies and would not be captured by an analysis restricted to antidumping.<sup>11</sup> In robustness checks, we also construct the count of products investigated under antidumping policy alone and we re-estimate the model using this dependent variable to illustrate the implications.

A second innovation in our approach is to examine data at the quarterly frequency; this is potentially important because macroeconomic shocks may cross calendar years. The key macroeconomic determinants of import protection in our model are bilateral real exchange rates, domestic unemployment rates, and the foreign trading partner’s real GDP growth, with each of the variables reflecting year-over-year changes at the quarterly frequency.<sup>12</sup> We define the exchange rate

> 9 These series derive from data in the World Bank’s _Temporary Trade Barriers Database_ (Bown, 2011b). Because the Harmonized System has been in place and utilized across countries only since 1988, the time series dimension of our data begins in 1988:Q1.

10 We focus on products subject to new investigations, given research from Staiger and Wolak (1994) which has shown that even an investigation can have trade-destroying effects. Nevertheless, in unreported results available from the authors, we confirm that the evidence below extends to a redefinition of the dependent variable to counts of products under investigations that only conclude with formal trade barriers being imposed.

11 This measure is carefully constructed for each policy-imposing economy by trading partner and by quarter in a conservative way that does not allow for redundancy. At any point in time in the sample period under the Harmonized System, there are roughly 5000 HS-06 imported products that could be imported from any particular trading partner. In terms of policy, governments impose these import restrictions at the 8- or 10-digit product level; unfortunately the HS-06 level is the most finely disaggregated level of data that is comparable across countries. First, so as to avoid double counting in cases in which new import protection at the 8-digit level falls into the same HS-06 category as a previously imposed barrier, we do not include such products. Second, for our baseline import protection measure that expansively covers all four TTB policies, we also do not include products that were subject to a simultaneous or previously imposed barrier under a different policy. This phenomenon is particularly relevant for countervailing duties as most have been imposed simultaneously with antidumping duties on the same products against the same trading partners. For a discussion, see Bown (2011a).

12 We are forced to use year-over-year changes in these variables as opposed to quarter-to-quarter changes due to how quarterly real GDP for China, one of the key trading partners in the analysis, is defined and available in the underlying data. Thus each of the key macroeconomic determinants is defined as a year-over-year change; i.e., quarter 1 of year _t_ over quarter 1 of year _t-1_ , quarter 2 of year _t_ over quarter 2 of year _t-1_ , etc.

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