mation source on international trade statistics, gathering export and import transactions (values and physical quantities) of firms located in Portugal by product category (CN classification, 8-digit) and destination or source market. These data are collected in two different ways. Data on trade with countries outside the EU (external trade) are collected via the customs clearance system, which covers the universe of external trade transactions. Information on the transactions with other EU member States (internal trade) are obtained via the Intrastat system, where the information providers are companies engaged in internal trade and registered in the VAT system whose value of annual shipments exceeds a legally binding threshold. Trade transactions in these data are _free on board_ , hence excluding any duties or shipping charges. Despite the above-mentioned constraint, the export and import transactions included in the FTS data aggregate to nearly the total value of merchandise exports and imports reported in the official national accounts.

The EIAS is a census of firms operating in Portugal run by the National Statistics Institute since 2005. Among other variables, it contains information on total employment, sales, wage bill, capital stock, value added, date of constitution, industry code and location. Using unique firm identifiers, we have linked the FTS and EIAS data sets for the years 2005 to 2009.<sup>5</sup> We have further used FTS data spanning the period 1990-2009 to compute exportage and export-destination-age. In each year, these variables are defined, respectively, as the number of consecutive years the firm has been an exporter in any market or an exporter in a particular export destination.<sup>6</sup> As is customary in the empirical trade literature, we restrict the analysis to firms whose main activity is in the manufacturing sector excluding the Petroleum industry. We impose these restrictions using the firm’s selfreported industry code in the EIAS data set, where sectors are defined by the Revision 2.1 of the National Classification of Economic Activities (CAE).<sup>7</sup> All nominal variables are expressed in 2005 euros, using the GDP deflator of Portugal.

Table A1 in the Appendix reports summary statistics. In line with evidence for several other countries (Bernard et al., 2007), we observe that exporters tend to be larger, older, more productive, more capital intensive and pay higher wages than non-exporters. The average exporter in the period 2005-2009 obtained 3.45 million euros of export proceeds, served 5.4 destinations and exported in 8.4 different product categories. Exporting firms sourced on average 2.23 million euros from other nations, distributed by a mean of 14.2 product categories and 3.5 different countries. The average exporter in the sample has 8.3

> 5In both the FTS and EIAS, firms are uniquely identified by their tax identification number (NPC). For statistical confidentiality reasons, the data made available to researchers contains anonymized unique identifiers (a transformation of the real NPC that has a one-to-one mapping to the real one). Hence the mapping of the two data sets was straightforward.

> 6 Since our measures of export experience are computed from trade-transactions data spanning the period 1990-2009, they are truncated at the difference between the reference year and 1990 (and hence are bounded by the upper limit of 20 years).

> 7Firms reporting their main activity to be in the manufacturing sector account for about 82.4% of total exports in the FTS data set for 2005-2009.

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