Finance and Economics Discussion SeriesDivisions of Research & Statistics and Monetary AffairsFederal Reserve Board, Washington, D.C.A Concordance Between Ten-Digit U.S. Harmonized SystemCodes and SIC/NAICS Product Classes and IndustriesJustin R. Pierce and Peter K. Schott2012-15NOTE: Staff working papers in the Finance and Economics Discussion Series (FEDS) are preliminarymaterials circulated to stimulate discussion and critical comment. The analysis and conclusions set forthare those of the authors and do not indicate concurrence by other members of the research staff or theBoard of Governors. References in publications to the Finance and Economics Discussion Series (other thanacknowledgement) should be cleared with the author(s) to protect the tentative character of these papers.

A Concordance Between Ten-Digit U.S. Harmonized SystemCodes and SIC/NAICS Product Classes and IndustriesJustin R. PierceyBoard of Governors of the Federal Reserve SystemPeter K. SchottzYale School of Management & NBERDecember 2011AbstractWhile the relationship between international trade and domestic economic activity is an important topic in economics, research in this area has been slowed due to data limitations. In this paperwe provide tools that improve the existing data in two ways. First, we develop an algorithm thatyields concordances between the ten-digit Harmonized System (HS) codes used to classify products in U.S. international trade and the SIC and NAICS industry codes used to classify domesticeconomic activity. These concordances then yield novel time series of industry-level internationaltrade data for the years 1989 to 2009. Second, we provide concordances between HS codes andthe SIC and NAICS product classes used to classify U.S. manufacturing production, allowing formatching at a more disaggregated level than was previously available.Keywords: International trade; industry classi cationJEL classi cation: F1We thank Julie Linden of the Yale University Social Sciences Library for generous help in securing thepublicly available U.S. trade data. We thank Kitjawat Tacharoen and Matt Flagge for research assistance.We thank Alvin Venning, Carol Ann Aristone, James Kristo and Mendel Gayle of the U.S. Census Bureaufor many enlightening conversations. Schott thanks the National Science Foundation (SES-0241474 andSES-0550190) for research support. The analysis and conclusions set forth in this paper are those of theauthors and do not indicate concurrence by the Board of Governors, other members of the research sta orthe National Science Foundation.yCorrespondence: 20th & C ST NW, Washington, DC 20551; email: [email protected]; telephone:202-452-2980; fax: 202-736-1937.z135 Prospect Street, New Haven, CT 06520, tel: (203) 436-4260, fax: (203) 432-6974, email: [email protected]

HS to SIC and NAICS1.2IntroductionEmpirical researchers in the elds of international trade and industrial organization areincreasingly focused on examining the relationship between international trade and domestic economic activity. This research agenda was rst pursued with industry-level data as inRevenga (1992) and Sachs and Shatz (1994). More recently, demand for linked trade andproduction data has increased along with the massive growth of research using highly disaggregated plant and rm-level data, as in Bernard, Jensen and Schott (2009) and Bernard,Redding and Schott (2010). Applied research in these elds has been slowed, however, dueto an inability to create long time series of industry-level international trade and productiondata or to match trade data to detailed product-level domestic data.In the U.S., international trade data have been classi ed since 1989 based on the WorldCustoms Organization’s Harmonized System (HS). In contrast, domestic economic activityhas been classi ed using the North American Industrial Classi cation System (NAICS)—beginning with the 1997 economic census— and the Standard Industrial Classi cation (SIC),prior to the 1997 economic census.1 This creates two potential di culties when linking tradeand production data. First, the HS classi es products solely on physical characteristics whileSIC and NAICS classify products based on physical characteristics and the type of economicactivity. Second, the switch from SIC to NAICS beginning with the 1997 economic censusmeans that it has been di cult to construct a time series linking trade and production datafor the entire period from 1989 to present.This paper improves on currently available data in two ways. First, we provide analgorithm that generates concordances linking the ten-digit HS codes used by the UnitedStates to track international trade with the four-digit SIC and six-digit NAICS industrycodes used to characterize domestic economic activity. These concordances are assembledfrom published U.S. Census Bureau (“Census”) data, which provide a mapping of HS to SICand NAICS industries from 1989 to 2001 and 2000 to 2009, respectively. Our contributionhere is to extend these mappings to match HS codes with SIC industries after 2001, and tomatch HS codes with NAICS industries before 2000. As a result, applied economists will beable to create— for the rst time— linked datasets of trade and domestic production in bothSIC and NAICS over a long time series–1989-2009 for NAICS and 1989-2006 for SIC.2Second, we provide a set of concordances linking ten-digit import and export HS codesto one or more ve-digit SIC (SIC5) or seven-digit NAICS (NAICS7) product classes. Theseconcordances are constructed using bridge codes known as “basecodes,”which are created bythe U.S. Census Bureau (“Census”). In each year of an economic census, Census constructstwo mappings linking HS codes to basecodes and linking basecodes to SIC5 or NAICS7 product classes, respectively. We combine the two mappings to directly link HS codes to productclasses. This set of concordances then allows researchers to match international trade anddomestic production data at a more disaggregated level than has previously been available.Each of the contributions in this paper improves the ability of empirical researchers to calculate measures of trade and domestic economic activity that are more directly comparableand hence more accurate for research purposes.12Each of these product classi cation systems is described in more detail in Section 2.The reason for the shorter time period for HS-SIC4 mappings is discussed in Section 3 below.

HS to SIC and NAICS3Finally, we brie‡y discusses how these concordances might be applied in current empirical international trade research. In particular, we provide background information useful forlinking the rm-product-class domestic production data in the U.S. Census of Manufactures(CM) to the rm-product import and export data in the Longitudinal Firm Trade Transaction Database (LFTTD). For more detail on the former, see Bernard, Redding and Schott(2010). For more detail on the latter see Bernard, Jensen and Schott (2009).The remainder of the paper is organized as follows. Section 2 provides a description ofthe HS, SIC and NAICS classi cation systems. Section 3 describes the HS to SIC4/NAICS6industry concordance, while Section 4 describes the HS to SIC5/NAICS7 product-class concordance. Section 5 discusses how the latter can be used to link Census production andtrade data. Section 6 concludes. Appendices provide the Stata code used to implement ouralgorithm and generate the concordances discussed in the paper and describe the key lesused to construct the concordances.2.A Description of the HS, SIC and NAICS Classi cation Systems2.1. Classifying Products in U.S. International Trade - The Harmonized SystemInternational trade data in all major trading countries— including the U.S.— is classi edbased on the Harmonized System developed by the World Customs Organization (WCO).The WCO begins by assigning products into 99 broad 2-digit categories such as chapter72, “Iron and Steel.” These chapters are then further broken out into 6-digit HS codes forcategories of goods such as heading 851670, which is de ned in the 2007 HS as “Co ee or teamakers.” Individual countries are then free to maintain more disaggregated classi cationsbeyond the 6-digit level.The U.S. maintains separate HS classi cations for imports and exports and classi esproducts at the ten-digit level. Import codes are provided in the Harmonized Tari Scheduleand maintained by the U.S. International Trade Commission (ITC). Export codes— formallyknown as “Schedule B” codes— are maintained by the Foreign Trade Division (FTD) ofthe U.S. Census Bureau. In this paper we refer to import and export codes generically asHS codes. For import HS codes, the ITC further aggregates the 99 chapters into 12 broad“sections,”which are listed in Table 1. The full listing of HS chapters and 10-digit HS importand export codes are available at websites of the ITC and FTD, respectively.2.2. Classifying U.S. Domestic Economic Activity - SIC and NAICSIn contrast to the HS, which classi es products based solely on their physical characteristics, SIC and NAICS are classi cations of business activities that incorporate productcharacteristics as well as the type of economic activity. SIC codes were used to classify U.S.economic activity until the Census Bureau’s 1997 economic census, with major revisions ofthe SIC occurring in 1972 and 1987. Starting with the 1997 census, U.S. economic activityis classi ed according to the NAICS, which is standardized for the rst ve digits across theU.S., Canada and Mexico.Census refers to the rst four digits of an SIC code, and the rst six digits of a NAICScode, as an industry. It reserves the terms product class and product for the rst ve and

4HS to SIC and NAICSTable 1: Import HS Sections and NameLive Animals; Animal ProductsVegetable ProductsAnimal or Vegetable Fats and OilsPrepared Foodstuffs; Beverages, Spirits, TobaccoMineral ProductsProducts of the Chemical or Allied IndustriesPlastics, Rubber and Articles ThereofRaw Hides, Skins, LeatherWood and Articles of WoodPulp of Wood, PaperTextile and Textile ArticlesFootwear, Headgear, etc.Articles of Stone, Plaster, Cement, Ceramics, GlassPearls, precious stones, precious metalsBase Metals and Articles of Base MetalMachinery, Appliances, Electrical EquipmentVehicles, Aircraft, VesselsPrecision InstrumentsArms and AmmunitionsMisc. Manufactured ArticlesWorks of ArtSpecial Classification 29394-969798-99Notes: This table displays sections and chapters U.S. Import HS Codes.Section names have been shortened for brevity. See the website ofthe U.S. International Trade Commission for full section digits of an SIC code, and the rst seven and ten digits of a NAICS code, respectively.While the set of o cial U.S. industries is de ned outside the Census Bureau, Census generallyhas discretion in de ning product classes and products within these industries. The primaryeconomic activity classi cations for both SIC and NAICS are provided in Table 2.There are a number of di erences between SIC and NAICS. First, NAICS provides moregranular industry de nitions than SIC, with the movement from 1,004 industries in SICcompared to 1, 170 industries in NAICS in 1997. Second, some activities were completelyreclassi ed in the switch from SIC to NAICS, such as printing and publishing, which wasreclassi ed from manufacturing (SIC 27) to wholesale trade (NAICS 51).2.3. Some Complications Associated With Mapping HS to SIC/NAICSAs mentioned above, the HS and SIC/NAICS systems are fundamentally di erent in thatthe HS classi es products based solely on physical characteristics, while SIC and NAICSincorporate physical product characteristics as well as the type economic activity. Thisdi erence between the two systems can perhaps be most easily seen through a speci c example. In the 1992 Schedule B codes used to classify U.S. exports, HS code 7215200000tracks exports of “other bars and rods of iron or nonalloy steel, cold-formed or cold- nished,less than 0.25 percent carbon.” While this de nition is based solely on physical characteristics, the SIC/NAICS product classes to which it matches also take into account the

5HS to SIC and NAICSTable 2: Import NAICS and SIC 5152535455SICDescriptionCategoriesAgriculture, Forestry, Fishing and Hunting01-09Mining, Quarrying, and Oil and Gas facturing41-49Wholesale Trade50-51Retail Trade52-59Transportation and Warehousing60-67Information70-89Finance and Insurance91-97Real Estate and Rental and LeasingProfessional, Scientific, and Technical ServicesManagement of Companies and EnterprisesAdministrative and Support and Waste56Management and Remediation Services61Educational Services62Health Care and Social Assistance71Arts, Entertainment, and Recreation72Accommodation and Food Services81Other Services (except Public Administration)92Public AdministrationNotes: Table displays the primary categories of economic activity inSource: U.S. Census Bureau.DescriptionAgriculture, Forestry, FisheriesMineral IndustriesConstruction IndustriesManufacturingTransportation, Communication, UtilitiesWholesale TradeRetail TradeFinance, Insurance and Real EstateService IndustriesPublic Administrationthe NAICS and SIC classification systems.method of production. In particular, this HS10, maps to two separate SIC5 product classes,33128— “cold- nished steel bars/bar shapes (made in mills)— and 33168— “cold- nished steelbars/bar shapes (not made in mills).The switch from SIC to NAICS for classifying domestic production also complicatesmatters. Because international trade data are reported in SIC format only for the years1989-2001 and in NAICS format only for the years 2000 to 2009, researchers have beenunable to construct a long time series spanning SIC and NAICS years. The concordancesprovided in this table allow applied economists to construct these long time series for theyears1989-2009 for NAICS and 1989-2006 for SIC.Lastly, HS codes are continually revised over time. Changes to the U.S. import or exportcodes occur via three routes: changes by the World Customs Organization (WCO) to theo cial list of international six-digit pre xes; U.S. legislation that a ects U.S. eight-digit codes(imports only); or changes by the Committee for Statistical Annotation of Tari Schedules(known as the “484(f) Committee”) to statistical ten-digit codes.3 For more information onchanges in HS codes over time, including a concordance tracking these changes, see Pierceand Schott (forthcoming).3See seminar pres.ppt, and for more detail.

HS to SIC and NAICS3.6Concording HS to SIC4/NAICS6 IndustriesAs described above, empirical researchers have been hampered by an inability to generatelong time series of industry-level international trade data and domestic production spanningSIC and NAICS years. This section describes an algorithm and concordances that we create,which link international trade and domestic economic activity data for the years 1989-2009.The concordances can be used to construct comparable datasets of international trade anddomestic production data for longer time series than have previously been available.The source data for the concordances is found in the monthly trade data published inCD format by Census’s Foreign Trade Division.4 Each of the monthly CDs for imports andexports contains a dBase-formatted le (called concord.dbf) that separately matches theten-digit import and export HS codes used in the month to four-digit SIC and/or six-digitNAICS codes. We refer to these four-digit SIC and six-digit NAICS codes as “baseroots”forreasons discussed in the next section, but they are almost always proper industries.5 Notethat the December CD for each year contains annual, as well as monthly totals.From 1989 to 2001, the mappings provided by Census match ten-digit HS codes to fourdigit SIC baseroots. From 2000 to the present, they match ten-digit HS codes to six-digitNAICS baseroots. But for certain applications, it might be useful to extend each set ofmappings beyond the years for which these o cial concordances are available. That is, itmay be useful to have an HS-NAICS6 concordance for years prior to 2000 or an HS-SIC4concordance for years after 2001.We extend the HS-NAICS6 mappings to cover the period from 1989-2009 and the HSSIC4 mappings for the years 1989-2006 using a three-step algorithm based on the proceduresused previously in Feenstra et al. (2002). The algorithm is implemented on a “master list”of concordances assembled by appending the HS-baseroot mappings contained in the annualDecember trade CDs for the years 1989-2009. Note that we do not provide HS-SIC4 mappingsfor years after 2006 because the number of SIC4 codes that need to be assigned by hand-step3 in the algorithm-rises to a level that makes the mapping less reliable, in our view.The Stata code for steps 1 and 2, and for incorporating the results of step 3, is availablein Appendix 1 under lename schott algorithm The Stata code for the algorithmwas created using Intercooled Stata, version 9.2 on a 2.0 GHz T2700 Intel Core 2 CPU. Thesteps of the algorithm are described immediately below.1. Step 1 (Mechanical Match 1): Examine all ten-digit HS within a nine-digit category.If all assigned ten-digit HS within this category have the same NAICS6 (SIC4) assignment, assign that NAICS6 (SIC4) to any unassigned ten-digit HS within that nine-digit4CDs are available starting in December, 1989 for exports and January 1989 for imports. The CDs areavailable for purchase from Census and are often also available in university libraries. The copies used hereare provided generously by the Yale University Social Sciences Library.5Of the 461 NAICS baseroots in the HS-NAICS6 import concordance and 455 NAICS baseroots in theHS-NAICS6 export concordance, 10 are not real industries as de ned in the NAICS. They are 11211X,1123XX, 31131X 31181X, 31511X, 33631X, 910000, 920000, 980000, 990000. Of the 471 SIC baseroots inthe HS-SIC import concordance, 5 are not real industries as de ned in the SIC. They are 314X, 9100, 9200,9800, 9900. Of the 470 SIC baseroots in the HS-SIC export concordance, 7 are not real industries. They are314X, 3XXX, 9000, 9100, 9200, 9800, 9900.6The le is also available electronically on Schott’s website: international.htm

7HS to SIC and NAICScategory. Repeat for eight-, seven-, etc. digit HS categories.2. Step 2 (Mechanical Match 2): Sort list by ten-digit HS code. Examine “gaps”consistingof HS codes, or groups of consecutive codes that have not been matched to a baseroot.If a gap is preceded and succeeded by the same NAICS6 (SIC4) code, use that NAICS6(SIC4) code for all unassigned ten-digit HS codes in the gap.3. Step 3 (Hand Matching): Hand match remaining unmatched HS codes where possible.Note that any remaining unmatched ten-digit HS codes account for a very small fractionof U.S. imports or exports.Tables 3 and 4 summarize the number of HS codes assigned using this procedure withSIC4 codes for years after 2001 and NAICS6 codes for years before 2000, respectively. Thedescriptions in the “source” column match those provided by the variable “matchtype” inthe les described in Appendix 2 below.Table 3: Extending the HS-SIC4 ConcordanceExport HSCodesImport HSCodesSource200220032004From Census16,04315,98915,915From Mechanical Match 11,1011,1841,289From Mechanical Match 2209215216From Hand Match293300308From Census7,9127,8867,883From Mechanical Match 1752768773From Mechanical Match 2132132134From Hand Match151151150Notes: This table displays the method used to assign SIC codes toafter 2001, when Census stopped reporting HS-SIC 7,8567,853839843134134150150HS codes for yearsTable 4: Extending the HS-NAICS6 ConcordanceExport HSCodesImport HSCodesSource19891990199119921993From Census10,46411,29311,63011,87412,057From Mechanical Match 12,9912,9812,8622,7112,599From Mechanical Match 2340317297263258From Hand Match607623625582588From Census6,7506,8747,1177,1177,200From Mechanical Match 1827769676673658From Mechanical Match 2143139137137137From Hand Match188189180180172Notes: This table displays the method used to assign NAICS codes to HS codes for yearsNAICS 22286914612099541990157149614350before 2000, the year in which Census began reporting HS-By aggregating the HS-baseroot mappings for all available years and extending them forthe full period in which the HS was in existence, we create HS to SIC4 and HS to NAICS6concordances for both imports and exports, for the period from 1989 to 2006 and 1989to 2009, respectively. See Appendix 2 for a full description of the nal concordance lesavailable in the electronic appendix to this paper.

HS to SIC and NAICS4.8Concording HS to SIC5/NAICS7 Product Classes4.1. Census’s Procedure for Mapping HS to SIC and NAICSResearchers in international trade and industrial organization have recently begun studying the role of changes in product mix on plant and rm-level performance, as well as examining how exposure to international trade can a ect rms’product mix. Examples of thisresearch include Bernard, Redding and Schott (2010), Pierce (2011), Bernard, Redding andSchott (2011) and Goldberg, Khandelwal, Pavcnik and Topalova (Forthcoming). With thisgrowing interest in product-level data, it is increasingly important to be able to match international trade and domestic production data at a highly disaggregated level. This sectiondescribes the construction of concordances that match ten-digit HS codes to ve-digit SICand seven-digit NAICS product classes–a more disaggregated level than has previously beenavailable to researchers.The primary bridge between HS and SIC (NAICS) product classes is a code referred toby the Census Bureau as a “SIC-base” (“NAICS-base”), which we refer to generically as“basecodes.”7 Basecodes are eight-digit alphanumeric codes that can generally be thoughtof as describing product characteristics. The rst four (six) digits of the SIC (NAICS)basecode represent the “root” industry of the basecode. We refer to basecode roots hereas “baseroots”and use them in constructing the industry concordances, as described in thepreceding section. The remaining digits are internal identi ers for whether the basecodeencompasses one or more product classes, and, in the latter instance, whether those productclasses are from di erent industries. For Census year 1992, enough data are available for usto also construct a HS to SIC5/NAICS7 concordance based on basecodes. For the 1997, 2002and 2007 HS to SIC5/NAICS7 concordances, however, we are restricted by data limitationsto matching HS and SIC/NAICS product codes through baseroots only. The di erencesbetween constructing concordances using basecodes versus baseroots are discussed in detailin the next sub-section.We match HS product codes to SIC5/NAICS7 product classes via baseroots using twocomplementary mappings produced by Census. The rst mapping, which we refer to here asan “HS-baseroot”concordance, assigns a single baseroot to each HS code. As noted above,these mappings are published in Census’s monthly releases of U.S. trade data on CDs. Thesecond mapping is known as the principle di erences (PD) le, which is constructed for everyeconomic census in years ending in 2 and 7. The PD le assigns a single baseroot to eachproduct class in the SIC or NAICS. HS product codes can then be matched to SIC5/NAICS7product classes through their baseroots. The HS-baseroot and PD mappings are discussedin detail in Appendixes 4 and 5 below, respectively.At this point, an example may be useful for xing ideas. In 1992, HS code 7215200000 wasused to track exports of “other bars and rods of iron or nonalloy steel, cold-formed or cold nished, less than 0.25 percent carbon.” According to the 1992 HS-baseroot concordance,this HS code – and 222 others – maps into SIC baseroot 3312. This baseroot, in turn,maps into 11 di erent SIC product class codes from 3 di erent four-digit SIC industries inthe 1992 PD le: 33121, 33122, 33123, 33124, 33126, 33127, 33128, 3312C, 33167, 33168 and7A more detailed discussion of Census’ SIC and NAICS concordance methods is available

HS to SIC and NAICS933170.8 We note that in the o cial Census ten-digit HS to four-digit SIC mapping discussedin Section 3, HS code 7215200000 maps uniquely to SIC industry 3312.This example highlights the “many-to-many” nature of the HS-product-class concordances. While each HS code maps to a single baseroot, many HS codes (223 in this example)can map to a single baseroot. Similarly, while each ve-digit SIC product class maps to asingle baseroot, many product classes (from three di erent industries, in this example) maymap to a single baseroot. As discussed in Section 5 below, the HS-baseroot and PD lescan be used to match the product classes U.S. manufacturing rms produce in each CMFyear to the products they import and export in those years.4.2. Matching on Basecodes Versus BaserootsMatching on baseroots is appealing because HS-baseroot mappings are available in allyears, allowing us to create concordances for every economic census year since 1992. Asnoted above, however, we have access to more disaggregated HS-basecode and SIC5-basecodemappings for 1992. The primary advantage of concordances using basecodes is a “moreprecise”mapping between HS and SIC5.To illustrate what we mean by “more precise”, consider once again HS code 7215200000,which we used to illustrate matching through baseroots in the previous sub-section. Asmentioned above, HS code 72150200000 and 222 other HS codes matched to 11 di erent SIC5product classes through baseroot 3312. When HS and SIC5 codes are matched through fullbasecodes, rather than baseroots, however, we nd that 7215200000 is one of only 10 HScodes that map to only two SIC5s –33128 and 33168, de ned under basecode 33128B00 –described as “cold- nished steel bars/bar shapes (made in mills)” and “cold- nished steelbars/bar shapes (not made in mills).”9 Because HS code 7215200000 is described as “otherbars and rods of iron or nonalloy steel, cold-formed or cold- nished, less than 0.25 percentcarbon”, it appears that assigning SIC5s based on a full basecode, rather than a baseroot,has provided a better match, by dropping unrelated SIC5 products like sheet and strip, pipeand tube and rails.HS code 7215200000 was matched to 9 additional SIC5s when we matched HS codes toSIC5 codes with baseroots versus basecodes. This matching of HS codes to additional SIC5swhen matching with baseroots is not uncommon, as illustrated in the following analysis of1992, the only year for which we can do both types of mappings. Of the 16,022 import HScodes in use in 1992, 9,289 are matched to additional SIC5s when using baseroot matching.The mean number of additional SIC5s matched to each import HS is 2.35. Similarly, ofthe 8,054 export HS codes in use in 1992, 5,396 are matched to extra SIC5s under baseroot8The product descriptions for these SIC5 product-classes are as follows: 33121 - Coke over and blastfurnace products; 33122 - Steel ingot and semi nished shapes; 33123 - Hot-rolled sheet and strip includingtin-milled products; 33124 - Hot-rolled bars and bar shapes, plates, structural; 33126 - Steel pipe and tubes(made in steel mills); 33127 - Cold-rolled steel sheet and strip (made in mills); 33128 - Cold- nished steelbars/bar shapes (made in mills); 3312C - Other steel mill products, including steel rails; 33167 - Cold-rolledsteel sheet and strip (not made in mills); 33168 - Cold- nished steel bars and bar shapes (not made in mills);33170 - Steel pipe and tubes.9Note that this example provides a good illustration of how HS codes may match to more than one SIC5,since the SIC considers the method of production when assigning product classi cations. The di erencebetween these product classes is whether or not they are made in steel mills.

HS to SIC and NAICS10matching. The mean number of additional SIC5s matched to each export HS is 2.72. Table5 displays the number of extra SIC5s associated with HS10 import and export codes for1992.Table 5: Additional SIC5s Associated With Each HS Under Baseroot MatchingExportsImportsHS10Additional SIC5HS10Additional 11171317120120324624427427Notes: Table displays the number of "Additional" SIC5sassociated with HS10 export and import codes in 1992.Additional SIC5s are SIC5 product codes that areassociated with a particular HS10 when a concordance isconstructed with 4-digit baseroots, rather than a full 8-digitbasecode.For some types of research, matching HS and SIC5/NAICS7 codes through full basecodesmight be useful. Pierce (2011), for example, identi es U.S. manufacturing establishmentsthat received antidumping protection by matching the HS10s used to classify products in antidumping investigations to the SIC5 product-classes that establishments reported producingin the CMF. In this case, matching on baseroots, rather than full basecodes, would likelylead to some unprotected plants being incorrectly identi ed as recipients of antidumpingprotection.Unfortunately, Census published a full HS10-basecode mapping only for 1992. As aresult, matching on basecodes can only be performed in a somewhat limited time period. Inthe electron

is classi–ed according to the NAICS, which is standardized for the –rst –ve digits across the U.S., Canada and Mexico. Census refers to the –rst four digits of an SIC code, and the –rst six digits of a NAICS code,