textiles and apparel and footwear, there is more variation across countries. The US has relatively high MFN applied tariffs in those sectors and has not used TTBs. On the other hand, Argentina, Brazil, India, Mexico and Turkey had these sectors protected by relatively high MFN applied tariffs and a relatively high import coverage by TTBs. One rationale for these countries, as we describe next, is frequently to address increased import competition in these sectors from other emerging economies, especially China (Bown, 2013b). Finally, chemicals and metals are relatively low tariff sectors but high TTB sectors, especially in high-income economies. This is consistent with use in earlier decades as we further detail below in Section 4. Contributing explanations include that these are high fixed cost, concentrated industries; this may affect an industry’s ability to organize politically and file petitions for TTB protection under these laws.

Here we briefly point to two recent approaches that researchers have used to explain elements of the cross-sectional variation in TTB use within countries. First, Bown and Crowley (2013b) examine US TTB use at the industry-trading partner level over 1997-2006 in order to assess whether import protection responds to terms-of-trade pressure, in the spirit of the repeated game model of Bagwell and Staiger (1990). Because US applied MFN tariffs are constrained due to WTO tariff bindings, the Bown-Crowley approach can be interpreted as providing evidence consistent with the terms-of-trade theory that levels of import protection increase in the face of trade volume surges, especially in sectors with import demand and export supply that are relatively inelastic. Second, Bown and Tovar (2011) examine India’s applied TTBs and the Grossman and Helpman (1994) model of endogenous trade policy formulation. Their empirical results are consistent with the Grossman-Helpman theory when using India’s applied MFN tariffs in 1990, inconsistent with the theory for applied MFN tariffs _only_ in 2000-2002, but consistent again with the theory when using India’s TTBs _in addition to_ the applied MFN tariffs in 2000-2002. This evidence suggests that, over time, India unwound some of its applied tariff reductions by substituting toward antidumping and safeguard policies.

The last of our thematic questions is whether, when countries apply import protection through TTBs, their applied policies discriminate among different trading partners. While there are different ways to examine this issue, Table 6 presents two measures - the trade-weighted share of the exporting country’s total exports to the G20 economies over which the G20 economy had a TTB imposed, and the estimated value of those TTB-impacted exports to the G20 economy.<sup>56</sup> We compute these two measures both in 2013 for the G20 economies and then, for rough comparison purposes, also in 1995 for the ‘G4’ economies of Australia, Canada, the EU and the US - the major TTB users at the time.

To interpret Table 6, consider an exporter like China. In 2013, 7.1 percent of China’s exports to the G20 economies were subject to a TTB, and this is estimated to cover roughly $100 billion of

> 56These data are derived from dynamic import coverage ratios following the methodology described and applied in Bown (2011b, 2013b). The main requirement is an assumption on counterfactual import growth for products from trading partners subject to an imposed TTB during the period that the TTB was in effect. The current data relies on the relatively conservative assumption that TTB-impacted products would have grown at the average rate of import growth for non-TTB impacted products.

32