U.S. antidumping investigations.<sup>13</sup> The fields we employ include ‘Customs value’, which measures the value of imports at the foreign port. We typically identify prices by deflating these values by a quantity measure, usually the ‘first unit of quantity’ as reported in the data.

Note that these data allow us to identify not only the products and countries that are subject to a petition, but also imports in the subject products from all sources (i.e. both named and nonnamed countries). This offers an opportunity to investigate the extent to which imports from the subject countries in the subject products are typical and in what ways they differ from the imports coming from other non-named sources. In addition we can identify a reference group of products that are similar to the subject products but that are not named in the petition. The group of related products serves as an important reference group in our attempt to understand why some products are subject to an AD petition and why others are not. In making these comparisons we track the value and quantity of imports in both named and reference products from subject and non-subject countries over the 24 months preceding the filing of an AD petition.

One issue that arises when following HS codes over time is that definitions change relatively frequently (for example over 4,500 new HS-10 codes were introduced between January 1994 and January 1996).<sup>14</sup> Since we analyze the shipments occurring in the previous 24 months, changes in product definitions can have a large impact on the amount of data available (for instance if the definition of a product changes in the month before an AD case is filed then only one month’s worth of data is available). To mitigate these problems we identify a period of time where the definitions of HS-10 products are relatively stable, 1998-2004.<sup>15</sup> Consequently, we are able to track almost all HS-10 product codes associated with the AD cases filed between 1998 and 2004 for 24 months preceding the filing of an AD petition.<sup>16</sup> We consider 106 investigations initiated in the 1998-2004 period.<sup>17</sup> An investigation often includes multiple countries, and each investigation-country pair is associated with the filing of a pe-

> 13The U.S. also reports _General Imports_ which measures total physical arrivals into the United States, including shipments bound for bonded warehouse or transshipment to other countries.

> 14A single HS-10 code can be replaced by a number of new codes or it maybe amalgamated with a number of other HS-10 codes. In either case the identifier associated with the old HS-10 code is deleted.

> 15This period is also of interest because it encompasses the adoption of the Byrd Amendment, a legal change that affected the incentives to file a petition.

> 16To evaluate the impact of HS-10 changes that do occur within our sample, we use the Pierce and Schott (2012) concordance mapping HS-10 changes over time. Since very few commodities are affected, there is little effect on the results. The bridging techniques in Pierce and Schott (2012) are not well suited to our exercise, as they tend to expand the product scope of the listed HS-10 products. We report results from a more conservative approach, which involves dropping those commodities that appear or disappear within the two-year window prior to each case we consider.

> 17111 investigations were initiated over this period. Three pairs of investigations are near duplicates, and we keep only one investigation of each pair. We also drop two investigations from the data set for lack of quantity information in the trade data. See the data appendix for a more complete discussion of our treatment of the data.

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