Carry-Along Trade∗
Andrew B. Bernard†
Tuck School of Business at Dartmouth, CEPR & NBER

Emily J. Blanchard‡
Tuck School of Business at Dartmouth

Ilke Van Beveren§
Lessius Department of Business Studies, KULeuven CES & LICOS,& National Bank of Belgium

Hylke Vandenbussche¶
IRES-CORE, Université Catholique de Louvain, KULeuven-LICOS,
National Bank of Belgium, & CEPR
This Version: July 2012∗
A special thanks goes to Jean-Marc Troch at the National Bank of Belgium for assistance and help with thedata. We are also grateful to Stefania Garetto, David Green and seminar participants at the NBER, ERWIT,
Dartmouth and UBC for helpful comments, Christophe Piette and Kris de Spiegelaere for data clarifications andDanny Delcambre for providing us with supplementary files and help with the CN concordance. Vandenbussche
thanks ARC, UCL and Excellence Centre LICOS for support. This paper was written while Van Beveren and
Vandenbussche were visiting the National Bank of Belgium. The views expressed in this paper are those of
the authors and do not necessarily reflect the views of the National Bank of Belgium, the National Bureau of
Economics Research or the Centre for Economic Policy Research. All remaining errors are our own.
†
100 Tuck Hall, Hanover, NH 03755, USA, tel: +1 603 646 0302,email: andrew.b.bernard@tuck.dartmouth.edu‡
100 Tuck Hall, Hanover, NH 03755, USA, tel: +1 603 646 8962, email: emily.j.blanchard@tuck.dartmouth.edu§
Korte Nieuwstraat 33, 2000 Antwerp, Belgium, tel: +32 3 201 18 33, email: ilke.vanbeveren@kuleuven.be¶
Place Montesquieu 3, 1348 Louvain-la-neuve, Belgium, tel :+32 10 47 41 37, email :hylke.vandenbussche@uclouvain.be1

Abstract
Large multi-product firms dominate international trade flows. This paper documents new
facts about multi-product manufacturing exporters that are not easily reconciled with existing multi-product models. Using novel linked production and export data at the firm-productlevel, we find that the overwhelming majority of manufacturing firms export products thatthey do not produce. Three quarters of the exported products and thirty percent of export
value from Belgian manufacturers are in goods that are not produced by the firm, so-called
Carry-Along Trade (CAT). The number of CAT products is strongly increasing in firm productivity while the number of produced products that are exported is weakly increasing infirm productivity. We propose a general model of production and sourcing at multi-productfirms. While the baseline model fails to reconcile the relationships between firm productivity
and the numbers of exported products observed in the data, several demand and supply-side
extensions to the model are more successful. Looking at export price data, we find support
for a novel theoretical extension based on demand-scope complementarities.
Keywords: heterogeneous firms, multi-product firms, exporting, sourcing, productivity,intermediation, demand-scope complementarity
JEL codes: F12, F13, F14, L11

Carry-Along Trade1

Introduction

Exports are well-known to be highly concentrated in a relatively small number of firms that ship
many products abroad. Existing models of multi-product exporters describe firms that makeone or more products and ship some or all of those products abroad.1

We present the firstevidence that these multi-product exporters are, in fact, not making most of the products thatthey export. Instead, the most productive firms both make and source products that they thensell to the market. In this paper, we explore this phenomenon both empirically and theoretically.
This research contributes to the small but growing literature documenting the prevalence andimportance of multi-product firms in international trade. Unlike most previous work on multiproduct firms, we are able to link data on domestic production and international trade at thefirm-product level. This allows us to compare domestic output and exports at the firm-productlevel. We document the surprising fact that a large majority of manufacturing exporters export
many products that they do not produce. In addition, a smaller set of the largest manufacturingfirms produce goods where they export more than they produce.

We refer to these export

activities together as Carry-Along Trade (CAT).
We find that Carry-Along Trade, i.e. exports of goods where the firm exports more thanit produces, is widespread and important, occurring at more than 90 percent of exporters,
appearing in more than 95 percent of exported products and accounting for more than 30
percent of export value.
While most firms export products they do not make, it is the most productive firms that are
most heavily engaged in Carry-Along Trade. Firm productivity has been shown to be positively
related both to the number of products made by the firm and especially to the number of products
exported.2 Our findings confirm those results but highlight the relationship between measuresof firm productivity and exported CAT products.

The total number of products supplied toexport markets is strongly increasing in firm productivity.

While more productive firms doexport more of their own produced products, most of the increase in export scope is due toa strong positive relationship between firm productivity and sourced (CAT) products that areexported. The share of CAT products in total exported products is rising in productivity.
Total firm exports are also known to be strongly positively associated with firm productivity.
In contrast to the number of products, the majority of export value does come from productsthat are produced by the firm. The share of CAT exports in total export value is much smaller
than that of produced products and does not systematically change with firm productivity.
1

Bernard et al. (2007) and Mayer and Ottavianio (2008) provide evidence on the importance of multi-productexporters. Theoretical models of multi-product exporting firms include Eckel and Neary (2010), Bernard et al.
(2011), Arkolakis and Muendler (2011) and Mayer et al. (2011).
2
See Bernard et al. (2011), Arkolakis and Muendler (2011) and Mayer et al. (2011).

1

Carry-Along Trade

To understand the observed phenomenon where firms sell more products to the market thanthey actually produce, we develop a general model of multi-product producers and sourcing.
Although the theoretical exercise is motivated by trade data, our model is intentionally designed
to study how firms serve markets, broadly defined. Our modeling approach is intrinsicallyagnostic so that we can consider a variety of potential explanations for Carry-Along Trade.
For each, we outline the plausible underlying cause of CAT, formalize the implied relationshipbetween CAT and firm characteristics, and then briefly evaluate the relative likelihood that themechanism is at play given observed patterns in the data.
Our model features heterogeneous, multi-product firms that face a two-tiered problem: tochoose the optimal product scope (how many varieties to sell to the market, and how much atwhat price for each variety), and a make or source decision – the question of whether (or towhat extent) to produce goods in-house versus through arms-length suppliers, i.e. CAT. In thespirit of Mrazova and Neary (2011), we focus on equilibrium selection among heterogeneousfirms – specifically the relationship between firm productivity, product scope, and the make-orsource decision margin – and purposely set aside derivation of the full general equilibrium. Thisapproach has the important advantage that we are not compelled to make specific functional
form assumptions, allowing us to develop a unified framework in which to identify and discuss
important differences among broad classes of both supply side and preference structures.
We adopt a three step approach to the theoretical exercise. We begin by outlining a simple
version of a multi-product heterogeneous firm model with a make-or-source decision. We observethat a broad class of models shares the common feature that core productivity and the extent
of Carry-Along Trade is sub-modular in a firm’s payoff structure. Intuitively, for any given total
number of products delivered to the market by a firm, productive firms will make a greater shareof those products in-house – and thus necessarily source fewer products via CAT – than will lessproductive firms. The empirical prediction from this baseline modeling structure is thus thatthe least productive firms would do the most Carry-Along Trade – which is the opposite of what
we observe in the data.
We go on to introduce simple extensions of the model, first on the supply side, then on the
demand side. In every case, we outline a set of necessary conditions that would have to hold for amodel to rationalize the key features of the data. Again, the intuition is straightforward: higher
productivity firms must have sufficiently greater total product scope than lower productivity
firms, in order for both in-house and sourced product scope to be increasing in firm productivity.
Many natural extensions of the basic multi-product model do not reconcile the theory withthe data. However, we find that it is possible to match the empirical facts through certain
adjustments to either the supply or demand side of the basic model.

2

Carry-Along Trade

On the supply side, allowing more productive manufacturers to have lower marginal costs
for sourced products can generate the positive relationships between firm productivity and thenumbers of both produced and sourced products. However, the positive correlation between
marginal cost of production and marginal cost of sourcing has to be “just right” and cannot beeither too strong or too weak.3 Alternatively, if more efficient producers also have more efficient
distribution networks, there can be a positive correlation between firm productivity and thenumbers of both produced and sourced products.
Turning to preferences, we introduce a novel set of preferences that exhibit demand-scopecomplementarity, i.e. the demand for a given firm-product increases in the total scope of productofferings by the firm. Again the complementarity must be sufficiently strong for the model toexhibit a positive relationship between firm productivity and both the number of produced andsourced products.
To evaluate the theoretical framework, we consider both evidence from the Belgian trade data
as well as case-based evidence from interviews with U.S. and Belgian manufacturing exporters.
The interviews weigh strongly towards an explanation based on demand complementarity, although some firms report CAT exports due to distribution or sourcing advantages. Looking
at data on export prices, we find evidence consistent with the presence of demand-scope complementarities: prices for a given firm-product are higher in markets where the firm exports agreater number of products, all else equal.
The rest of the paper is organized as follows. In the next section we discuss the trade data anddemonstrate the prevalence and importance of multi-product exporters in total Belgian exports.
In Section 3, we explore the relationship between domestic production and exports in a sample
of Belgian manufacturing firms and examine how firm characteristics vary with the number ofexported products. Section 4 introduces definitions of Carry-Along Trade and documents that
CAT is widespread and important for firms, products and aggregate export value. In section
5, we examine the relationship between CAT and firm characteristics. Sections 6-8 present abasic model of multi-product firms and sourced products and extensions needed to match thestylized facts about CAT. We consider empirical implications of the theoretical framework anddiscuss evidence from case studies of exporting firms in Section 9. The final section concludes.

2

Multi-Product Exporters in Belgium

To develop a more complete understanding of the relationship between a firm’s production andexports, we link data from two different sources: one which records activities related to a firm’s
3

We refer to this as a “Goldilocks” result after
http://en.wikipedia.org/wiki/The Story of the Three Bears .

3

theBritishandAmerican

fairy

tale,

see

Carry-Along Tradedomestic production by product and another which tracks a firm’s exports by product. The
Belgian export data are obtained from the National Bank of Belgium’s Trade Database, which
covers the entire population of recorded trade flows. The export data are recorded at the yearfirm-product-country level, i.e. they provide information on firm-level export flows by 8-digit
Combined Nomenclature (CN8) product and by destination country. In our empirical work weconsider 6-digit product categories to facilitate comparison with datasets from other countries
and to reduce the likelihood of product misclassification.4
We exclude transactions that do not involve a “transfer of ownership with compensation”.
This means that we omit transaction flows such as re-exports, the return, replacement andrepair of goods, and transactions without compensation, e.g. government support, processing
or repair transactions, etc. We further exclude export product classes that do not correspondto activities in the production data.5 The remaining transactions cover more than 73 percent
of total reported export value for 2005.
In Table 1 we report summary statistics on the cross-section of exporting firms for 2005.
We categorize firms according to the number of six-digit products they export. In subsequentcolumns we include the number of firms, the value of exports, and the average number ofexport destinations for all firms exporting the reported number of products. In 2005 there are
20,848 exporting firms including both manufacturing and non-manufacturing firms operating inall sectors.

Total value of exports at these firms is over e195 billion representing more than712,000 firm-product-country transactions.6
Table 1 shows that multi-product exporters constitute the large majority of firms. Over66 percent of all exporters are multi-product (MP) firms and they account for 98 percent of
the total export value in 2005. Single-product exporters account for 34 percent of firms but
represent only 2 percent of exports. These numbers are comparable to those for other countries;
58 percent of US exporters are multi-product and account for more than 99 percent of exports(see Bernard et al., 2007). Relatively few firms export more than 20 products but these 11
percent of firms still account for 45 percent of exports. These results are very much in line withwhat was reported by Bernard, Redding and Schott (2011) for the US, Mayer and Ottaviano(2008) for France and Goldberg et al (2010) for India and confirm the notion of “superstar”
exporters where a small club of firms account for the large majority of exports.7
The average number of export destinations per firm is 7.15, but this average hides substantial
4

The CN classification is available at the Eurostat Ramon server: http://ec.europa.eu/eurostat/ramon/ .
For examples of these types of products and for a more complete discussion of the issues in combining EU
production and trade data, see Van Beveren et al. (2012).
6
The number of exporters in 2005 is very close to the average number of exporters for the period 1998-2005.
7
Results are different for Mexico where most exports come from single product exporters (Iacovone and Javorcik, 2010).
5

4

Carry-Along Tradeheterogeneity across firms. Firms that export just one product ship it to only 1.82 destination
markets whereas firms exporting more than 50 products on average reach 25 different destinations. This finding is in line with evidence from other countries and recent theory papers on
multi-product exporters where firms with higher firm productivity export more products andreach more destinations.8 A common feature of these models is that firms with higher productivity produce greater numbers of products, have higher total sales and larger total firm exports,
and export more products.

3

Manufacturing, Domestic Production and Exports

We now focus our attention on a sample of Belgian manufacturing firms where we can linkproduction and exports at the firm-product level for 2005.

The focus on manufacturing ex-

porters is driven by existing multi-product theory models which assume that a producing, ormanufacturing, firm produces one or more products and exports some or all of its produced
products. Recent work on trade intermediaries highlights the role of non-manufacturing firms inaggregate exports, see Bernard, Jensen, Redding and Schott (2010), Ahn, Khandelwal and Wei(2011), Akerman (2010), and Bernard, Grazzi and Tomasi (2011). However, in these papers,
manufacturing firms either export directly or through a non-manufacturing intermediary.
The theoretical literature on multi-product exporters is largely related to the joint productionand export decisions of the firm and typically does not consider the role of intermediation. The
existing empirical literature on multi-product exporters usually examines trade data alone ortrade and production data separately.9

We link export data to production data at the firm-

product level.
The firm-product production data come from the Prodcom database.
are the same as described in Section 2.

The export data

The Prodcom survey is used by Eurostat to collectcomparable industrial production statistics across EU countries and several special attributesof the Prodcom database are worth noting here.

First, two main types of firms are required

to declare their domestic production activities at firm-product level and thus are present in
the database: (1) firms with a primary activity in manufacturing employing at least ten employees and (2) firms with a primary activity outside manufacturing (but with manufacturing
production) employing more than twenty employees.10 Second, the variable we use to quantify
domestic production by product is firm-product sales of produced goods rather than the value of8

Models of multi-product exporters include Eckel and Neary (2010), Bernard, Redding, and Schott (2011),
Arkolakis and Muendler(2011), Mayer, Melitz and Ottaviano (2011).
9
An exception is Iacovone and Javorcik (2010) who consider both production and exports in Mexico. Theirdata come from a Monthly Industrial Survey that is unlikely to record information about exports of goods thatare not produced by the firm.
10
We examine a single year, 2005, in the remainder of the paper.

5

Carry-Along Trade

physical production in that year. Third, while trade transactions are reported using the 8-digit
CN classification system (CN8), domestic production activities are reported in Prodcom 8-digit
codes (PC8). While the CN8 and PC8 classifications are designed to be similar and to allow
product-level comparisons (see the data appendix and Table 4), the level of detail of the PC8 islower than that of the CN8.
We choose to concord the two product classifications into categories that correspond as closely
as possible to six-digit Harmonized System products (HS6). In particular, every product in ourempirical analysis is either a unique HS6 category or a collection of related HS6 categories. In
particular, there are 9,157 CN8 codes and 4,784 HS6 codes compared to 4,220 PC8 codes. Out of
the 4,220 PC8 codes, 2,140 have a one-to-one match with a single HS6 product. The remaining
PC8 codes are many-to-one mappings from PC8 to HS6 (423 HS6 codes), one-to-many mappings(1750 HS6 codes) or many-to-many mappings (471 HS6 codes). We concord the PC8 productdata to HS6 and henceforth refer to the 6-digit data as HS6+. Overall, there are 2,923 HS6+
products that feature in our data (either domestically produced or exported).
After linking the export and production datasets we have a sample of 3,631 exporting firms
with e85.0billion of exports in over 192,000 firm-product-country transactions in 2005, accounting for 17 percent of Belgian exporters and 43 percent of total Belgian exports in these products.
Among firms with a primary 2-digit NACE classification in manufacturing, the Prodcom sample
accounts for 58 percent of exporting firms and 91 percent of total exports.11 Table 2 reportssummary statistics for these firms by the number of HS6+ products exported. Given the selection criteria, it is not surprising to find that firms in this sample are larger in terms of thenumber of products exported, total value of exports, and average number of destinations thanthe broader set of firms in Table 1.
Looking across firms with different numbers of exported products, we find similar patterns
to those for the complete set of Belgian exporters considered earlier. Exports per firm and theaverage number of destinations are increasing as the number of exported products rises.
The last three columns of Table 2 use balance sheet data to study the link between thenumber of exported products and indicators of firm-level productivity and size.12 We confirm
findings from other research that firm productivity, value-added and employment are all higher
11

While all the firms in the Prodcom sample report positive manufacturing production, 521 exporting firms
have a non-manufacturing sector as their primary NACE 2-digit activity in the annual accounts data. Our results
on CAT trade are not affected by the inclusion or exclusion of these firms. Another 1,834 firms with positive
manufacturing in the Prodcom data are non-exporters.
12
Selection on availability of firm-level characteristics such as employment, value-added, tangible fixed assets
etc. imposes another restriction on the sample selection, i.e. only those firms with positive values for all firm
characteristics can be included in the analysis. To obtain comparable levels of total factor productivity (TFP)
across firms, we apply the Caves et al. (1982) methodology. Hence, TFP is calculated as an index, calculated bycomparing each firm to a hypothetical firm, where the hypothetical firm is defined as the average over all firms
in a two-digit NACE sector.

6Carry-Along Tradefor firms that export more products.

3.1

Exported versus produced products

The most unusual finding from this simple overview comes in column 2 of Table 2. Except forthe category of single-product exporters, firms in every other category report greater numbers of
products exported than products produced.13 Multi-product exporters are also multi-productdomestic producers but the number of exported products increases much more rapidly than thenumber of produced products, see Figure 1.

Figure 1: Exported Products and Produced Products, 2005
It is this simple fact that firms export more products than they produce that we explore
for the rest of the paper. We develop a set of facts about the relationship between domestic
production and exports at the firm-product level, discuss possible explanations including data
error, explore robustness of the findings and examine the relationship between firm productivity
and trade costs on the margins of trade for different types of products: those produced by thefirm and exported and those exported but not produced by the firm.14 Finally we present a
13
Production refers to sales of produced goods rather than the physical creation of the goods during the year.
This concept of produced sales corresponds more closely to the recorded export numbers and helps to avoid
problems of stockpiling and inventories.
14
We are not able to ascertain whether these sourced products are produced by other domestic firms at home7

Carry-Along Trademodel to explain the facts and examine its implications for the data.

4

Carry-Along Trade

To guide our exploration of what firms make and what they sell or export, we first introduce
a set of definitions of Carry-Along Trade for both products and firms. Products fall into threemutually-exclusive categories at the firm-product level: (1) non-exported firm-products which
are reported as produced by the firm but are not recorded as exports; (2) regular export firmproducts which are products both reported as produced by the firm and exported by the firm
and where the recorded value of exports is less than or equal to the value of production; (3)Carry-Along Trade firm-products which are products where the value of exports is greater thanthe value of production by the firm,#exported products = #regular + #CAT.
Carry-Along Trade (CAT ) firm-products can be further divided into two non-overlapping, exhaustive categories: (3a) pure-CAT firm-products where the firm export value is positive but
there is no recorded production in that product (domestic produced salesf p = 0), and (3b)mixed-CAT firm-products where the firm reports positive production and exports and the valueof exports is greater than that of production.

The number of exported products for eachfirm is the sum of types (2)-(3) while the number of produced products is the sum of types(1)+(2)+(3b),#produced products = #non-exported + #regular + #mixed-CAT.
Exporting firms can be divided into groups as well: regular exporters export only regular
products while Carry-Along Trade (CAT ) exporters export at least one CAT product and may
also export regular products,#exporters = #regular exporters + #CAT exporters.
Finally, we can split the value of aggregate exports, X =P

f Xf , by these manufacturingfirms into components related to CAT and Regular firm-products. We report information about
two different splits of firm exports. First we focus on the firm-products themselves. Total firm
exports is the sum of the value of exports of regular products, Regular exports, and the valueof exports of CAT products,
X
Xf =Xf p =p

X

Xf p +

p∈regularX

Xf p .

p∈mixed or pureCAT

or by firms abroad, i.e. whether this phenomenon is part of domestic or global supply chains.

8Carry-Along Trade

A second method allocates firm exports into produced exports, P Xf , and sourced (or nonproduced) exports, SXf . Produced export value is the sum of Regular exports and the value of
mixed CAT exports that are reported produced by the firm. Sourced exports equal the sum of
all pure CAT firm-product exports and the portion of mixed CAT exports that are not producedby the firm:

Xf

=

X
p

=

X

Xf p =X

P Xf p +p∈regular

X

Xf p

p∈CAT

p∈regular

XX

Xf p +P Xf p +p∈mixed CAT

SXf p +X

SXf pp∈pure CATp∈mixed CAT= P Xf + SXf .
In column 1 of Table 3 we explore Carry-Along Trade at the HS6+ level.
before, we have 3631 exporting firms in the concorded dataset.

As mentioned

Most of these exporters are

CAT exporters, 3233 or 89.0 percent. Indeed, most exporters, 3177, export at least one pureCAT product, i.e. a product where they report no domestic production.

CAT products areas pervasive as CAT exporters. Of the 2858 total unique HS6+ products (exported + nonexported), 2822 (98.7 percent) are reported as Carry-Along Trade by at least one firm.
While most firms export at least one CAT product and most products are exported as CAT
by at least one firm, the share in the total value of exports is lower. Exports of CAT products
account for e41.5billion or over 48 percent of the value of exports at these manufacturing firms.
Sourced exports are e25.4billion, just under 30.0 percent of total exports for these firms. PureCAT products account for 96 percent of the number of CAT products and 74 percent of thevalue of sourced exports.
These results suggest that the traditional image of a manufacturing exporter that produces
products and exports some or all of them is missing an important component.

The large

majority of products exported by the firm are not made by the firm and these sourced products
account for a sizable fraction of firm export value.

4.1

Data Issues

Ideally to compare production and exports at the level of the firm–product, one would like to havedata from a single source with both production and exports recorded in a common classification

9

Carry-Along Trade

system.15

For the combined production and export data, the export information is obtained

from a combination of surveys for Intra-EU trade and customs records for exports to non-EU
destinations and is based on the CN8 classification system, while the firm-product production
data comes from a survey of manufacturing firms and is based on the PC8 classification system.
It is possible that the same product might be classified in different 8-digit codes for the export
records and production records. If there is some ambiguity about the correct classification fora product, different individuals filling out the different forms and surveys may choose related
but distinct product classifications for the export and product information. Even the same
individual faced with different product descriptions might record the same good in two different
categories.
This can be seen in the context of a specific example from the CN and PC Codes and Descriptions for “Sweet Biscuits” in Table 4. Items in the HS6 category of “Sweet biscuits” can beclassified into five different CN8 categories depending on whether they are coated with chocolate/cocoa, the weight of the immediate packaging, the level of the milk-fat content, and whether
or not they are sandwich biscuits. There are two PC8 codes that encompass sweet biscuits basedon the chocolate/cocoa covering.

The CN8 codes map fairly simply into the PC8 codes but

mistakes in classification are still possible.

In such a case a slightly more aggregate view ofthe data will merge related product codes and eliminate spurious CAT exports. Our choice of asix-digit level of aggregation should remove many such cases of spurious misclassification.
In the remaining columns of Table 3, we examine how the prevalence of CAT trade changes
at different levels of aggregation. Column 2 reports the same numbers after having aggregatedboth the production and the export data to the HS 4-digit level. This represents a substantial
reduction in the number of categories as there are now only 1012 “products”.

Even at thismore aggregate level we find that CAT firms and products are pervasive. 84 percent of firms
export at least one CAT product and 98 percent of products are exported as a CAT product byat least one firm. Aggregating the product categories does reduce the value of exports of CAT
products by more than 15 percent to e34.3billion.
Aggregating further to the 2-digit level (90 “products”) continues to reduce the number
of CAT firms and the value of CAT exports.

However, even with extremely aggregated 2-

digit categories, 2669 firms (73 percent) report exporting in a category where they report no
production and the export value of CAT products is more than a third of the total export valueof these manufacturing firms. Our conclusion from this aggregation exercise is that product15

The preferred data are often administrative data which are collected in the normal course of business, e.g.
records developed for social security payments are useful sources of wage and employment information at theestablishment, as well as whether or not the establishment is in operation. Export values by product, firm anddestination are often administrative data as they are collected from mandatory customs forms.

10Carry-Along Trade

misclassification might play a role in some CAT exports but the phenomenon is widespread
across firms and products and represents a substantial fraction of exports by manufacturingfirms.
As an additional check of the robustness of the main facts about Carry-Along Trade, we
consider a range of different samples of the data as reported in Table 5. Concerned that firms
with large non-manufacturing operations might be distorting our results, we select firms witha primary activity in manufacturing and find no differences in the importance of CAT acrossfirms, products or the value of exports. The results are not driven by the presence of any
particular sector. For example, dropping firms in food-related manufacturing (a sector wherelarge wholesaler/retailers are likely to perform some manufacturing) does not alter the results.
One possibility is that firms are part of larger domestic or multinational group and might beexporting products made by other companies in the group. Dropping firms in either domestic
or foreign groups does not appreciably reduce the presence of CAT.16
Another potential data error comes from combining six-digit products into larger categories.
Including only products with a one-to-one concordance between the two 8-digit classification
systems again does not noticeably alter the fractions of CAT exporters and CAT products or
the CAT share of export value. We exclude any role for firm imports to avoid concerns that
CAT is primarily the result of re-exporting that is not correctly captured by customs procedures.
Again the results are not altered. In the final column, we see that the findings are robust to achange in the definition of CAT at the firm-product level, excluding the possibility that small
differences in reported production and trade numbers are generating CAT.17
While the possibility remains that some fraction of CAT trade appears in the data due
to misreporting or other measurement issues, the pervasive nature of CAT across firms andproducts is a robust stylized fact. In the next section, we report characteristics of regular andCAT exporters and examine the relationship between firm productivity and regular versus CAT
exports.

5

CAT and Firm Characteristics

Table 6 reports means of a variety of firm characteristics for all exporters, regular exporters andCAT exporters.

The second and third categories are mutually exclusive and span the set ofexporting firms.
16

Multinational and foreign-owned firms are defined using the FDI survey (cfr. Data Appendix). Domestic
groups are identified using ownership information from the Belfirst Database (BvDEP, 2006).
17
Firm-product exports are considered to be regular exports if the ratio of production to exports is greater than
0.99 and firm-product exports are consider to be pure CAT if the ratio is less than 0.01. Adjusting these cutoffs
does not materially change the importance of CAT across firm and products.

11

Carry-Along Trade

A quick comparison of columns 2 and 3 reveals that the relatively low number of regular
exporters are substantially smaller, less export intensive, and less productive than the CAT firms.
On average, CAT exporters employ four times as many workers, have value-added more thanfour times larger and export more than eight times as much. However, the much greater export
to production ratios at CAT exporters are driven by the CAT exports themselves; produced
exports to produced sales ratios are about 0.33 for both regular and CAT exporters even though
CAT exporters also export more regular products.
Revenue-based productivity measures, both TFP and value-added per worker, are 5-9 percent
higher at CAT exporters who also reach many more export destinations. In addition, CAT firms
display different ownership characteristics. CAT exporters are more likely to be part of a Belgian
multinational, i.e. a Belgian firm that has at least one foreign subsidiary of which it owns atleast 20 percent either directly or indirectly.

CAT exporters are also more likely to have aforeign shareholder that directly or indirectly owns at least 20 percent of the firm.

5.1

CAT, Margins of Trade and Productivity

In this section, we follow the empirical strategy of Bernard, Redding, and Schott (2011) andrelate the margins of firm trade to proxies for firm productivity.

Total firm exports can be

decomposed into the number of distinct products exported, Pf and the average exports per
product, X̄f ,Xfwhere X̄f

= Pf X̄f
1 X
Xpf .
=
Pf p

(1)

Previous empirical work on US exporters has shown a strong positive correlation between
measures of firm productivity and total exports as well as a positive relationship between productivity and the number of exported products (Bernard, Redding, and Schott, 2011).18 These
results also hold for total firm exports in our sample of Belgian manufacturing exporters. In
panel A of Table 7 we report pooled cross-section regressions for 2005 of log firm exports andits two constituent components on log firm TFP and fixed effects for the major industry of thefirm,
ln Yf = c + β ln Prodf + δi + εf(2)where Yf refers to the two components of the decomposition given by (1), i.e. Pf , and X̄f .
By construction the specification only examines the relationship of productivity and exports
18

We focus in this paper on the number of products and the average exports per product. Results including
the number of destinations as an additional extensive margin do not change the main results and are available
upon request.

12

Carry-Along Tradefor current exporters.

Firm exports are strongly positively associated with firm productivity

with an elasticity significantly greater than 1. Looking at the extensive and intensive margins,
we find positive and significant coefficients for the number of products, and the average valueof exports per product.

More productive firms export more products and ship more of eachvariety.
However, our interest lies in the differential response of regular exports and CAT exports.
In panels B and C of Table 7 we report a pooled cross-section regression for 2005 of log firm
exports of type j and its constituent components where the export type is either regular or CAT
on a dummy for export type, dCAT = 1 for CAT exports , a proxy for firm productivity, and aninteraction term including fixed effects for the major industry of the firm,ln Yfj = dCAT + β ln Prodf + γdCAT · ln Prodf + δi + εf(3)where Yf refers to the two components of the decomposition given by (1), i.e. Pfj and X̄fj .
Panel B of Table 7 uses log TFP as the firm productivity measure while panel C uses log
value-added per worker; the results are very similar for the two measures. Looking across thesecond row of coefficients in each panel, we find that the value of regular exports again increases
in firm productivity. However the rise in regular exports is due mostly to the rise in the averageexports per product; the number of regular products increases weakly with firm productivity.
CAT exports are significantly lower than regular exports within the firm (the CAT dummy isnegative and significant), however, they increase at a similar rate as firm productivity rises so theshare of CAT exports in total exports in not changing systematically with firm productivity.19
However, both the levels and the response to firm productivity is quite different across theextensive and intensive margins. The number of CAT products is greater than regular products
and increases much faster in firm productivity (column 2). The share of CAT products in totalexported products rises as firm productivity increases. Figure 2 shows the relationship between
the number of products, regular and CAT, and firm productivity. Average shipment size for
CAT products is lower than that for regular products and increases at a much slower rate as
firm productivity rises.
While the value of both regular and CAT exports increases with firm productivity, there
are notable differences between the responses of produced and sourced products. The increase
in regular export value comes largely through sizable increases in average shipments of eachproduct and much less through an increase in the number produced products that are exported.
For Carry-Along Trade, higher productivity is associated with increased export levels, but theincrease is split roughly evenly between rising numbers of CAT products and an increase in
19

The relationship between firm productivity and CAT exports can be obtained by summing the coefficient on
the productivity measure and that on the interaction term.

13

Carry-Along Trade

Figure 2: Productivity and Exported Products, 2005
average export value. The overall increase in exported products at more productive firms is due
mostly to adjustments in the number of CAT products.20
One potential issue stems from the use of log TFP or log value-added per worker as theproxy for firm productivity.21 We are less concerned about finding the perfect measure of productivity and are more interested in documenting robust relationships between firm efficiency
in production and the number and value of produced and sourced products. Table 8 repeats
the regression with the number of export products as the dependent variable with a set of additional firm characteristics that are likely to be positively correlated with underlying productive
efficiency. We consider as proxies, total production by the firm and production of the largest
product as well as total exports and exports of the largest product. Again we find that boththe number of regular export products and the number of CAT export products are increasingin the level of the firm productivity proxy. In addition the number of CAT products increases
20
Adding log employment to the specification reduces the magnitude of the coefficients on productivity but thepattern of results is largely unchanged. Similarly running the regressions with regular and pure CAT products
does not change the findings.
21
There are many issues in constructing measures of firm-level productivity, see Foster, Haltiwanger, andSyverson (2008) for comparisons of quantity and revenue-based TFP and de Loecker (2011) and Bernard, Redding
and Schott (2009) for some of the difficulties in constructing productivity measures for multi-product firms. The
presence of sourced products adds yet another set of potential problems in multi-factor productivity measurement.

14

Carry-Along Trademuch more rapidly than does the number of regular export products.

6

A Model of Multi-Product Firms and Sourcing

To our knowledge, the phenomenon of manufacturing firms exporting goods that they do not
produce themselves is not present in either the theoretical or empirical literatures on international trade. While there has been work on the role of networks in facilitating trade, e.g. Rauch(2001), Rauch and Watson (2004) and Petropoulou (2007), and the presence of intermediaries
in trade, e.g. Ahn, Khandewal and Wei (2011) and Akerman (2010), the typical assumption
in that recent empirical and theoretical work is that the intermediary is a non-producing firm.
Our work differs from and complements that new research by exploring the role of sourced andproduced products in the manufacturing exporter’s portfolio.

In this section, we present amodel of multi-product exporters that aims to explain the presence of CAT and its relationshipto firm productivity.
Notably, there is nothing intrinsically ‘international’ about the model. Rather, we examine
the choice between producing and sourcing a variety from the perspective of how firms best serve
markets. We are also silent on whether the sourced varieties are produced by domestic firms orimported. When we return to the data in a later section, we exploit the multi-market dimensionof the trade context to explore further the implications of our more general theoretical exercise.

6.1

Our Approach

Our goal is to construct a framework to identify the potential mechanisms and motivations
underlying Carry-Along Trade (CAT). To this end, our model features multi-product firms thatface a two-tiered problem: to choose the optimal product scope (how many varieties to sell tothe market, and how much at what price for each variety), and a make-or-source decision –the question of whether (or to what extent) to produce goods in-house or through arms-length
suppliers. The model is not one of vertical integration or intermediate products per se, though
we readily acknowledge the relevance of supply chain integration.
Because we are the first to identify the CAT phenomenon, we start from a blank slate in
our effort to explain it. Our modeling approach thus is designed to maximize both breadthand generality. We take an ex-ante agnostic approach to the potential sources of CAT, working
through a range of potential explanations. For each, we outline a plausible underlying cause ofCAT, formalize the implied relationship between CAT and firm characteristics, and then briefly
evaluate the relative likelihood that the mechanism is at play given observed patterns in the
data.

15

Carry-Along Trade

In the spirit of Mrazova and Neary (2011), we focus on equilibrium selection among heterogeneous firms – specifically the relationship between firm productivity, product scope, and the
make-or-source decision – and purposely set aside derivation of the full general equilibrium. Thisapproach has the important advantage that we are not compelled to make specific functional
form assumptions, allowing us to develop a unified framework in which to identify and discuss
important differences among broad classes of both supply side and preference structures.22
We adopt a three step approach to the theoretical exercise. We begin by outlining a simple
version of a multi-product heterogeneous firm model with a make-or-source decision. We observethat a broad class of models necessarily predicts a relationship between firms’ core productivity
and the extent of Carry-Along Trade that is in direct contradiction to the data. That is, thetheory predicts that the most productive firms would do the least Carry-Along Trade, while thedata clearly indicate the opposite. From this we conclude that that there must be somethingelse at play, and thus proceed through a series of potential explanations. We focus first on
supply-side mechanisms, before shifting attention to demand. For each modeling alternative, weoutline a set of necessary conditions that would have to hold for a model to rationalize the key
features of the data.

6.2

The Baseline ModelFirms. Our general framework features a continuum of atomistic firms, indexed by j ∈ [0, 1],each of which may provide (potentially) multiple unique varieties to the market.23 Each firm
has a ‘core’ variety indexed by i = 0; remaining varieties are indexed by their distance from thecore according to i ∈ (0, kj ], where kj denotes the (endogenous) equilibrium mass of varieties
provided to the market by firm j. Each product in the market is uniquely identified by thefirm-variety pair, ji.
Firms can serve the market in three ways: by producing in-house, by sourcing from armslength suppliers, or some combination of the two – producing some goods, and sourcing others.24
We assume constant returns to scale in both in-house production technology and in arms-length
sourcing costs so that within a given variety all goods will be either produced in-house or sourced
22
Moreover, as is well recognized in the literature and eloquently argued by Mrazova and Neary (2011), derivation of closed form general equilibrium outcomes generally requires not only specific functional form assumptions,but very particular functional form assumptions for tractability. The most tractable frameworks also carry anumber of idiosyncratic, albeit convenient, properties that we prefer to avoid.
23
We treat firms as atomistic within the industry for analytical convenience. Market power could be incorporated
into the model, as in Eckel and Neary (2010), without fundamentally changing our qualitative findings. Firmlevel market power at the industry level is loosely analogous to the ‘quantity cannibalization’ extension consideredin section 8.2.1, which implies a relationship between CAT and firm productivity exactly the reverse of what we
observe in the data.
24
Firms that source all goods, i.e. pure wholesalers, are not in our sample, while firms that produce only
in-house, “regular firms”, are relatively few in the data. See Table 5.

16

Carry-Along Tradefrom arms-length suppliers, but not both (except the razor’s edge variety with identical in-houseand sourcing costs).25 We refer to goods produced in-house as regular goods, and goods sourced
from arms-length suppliers as carry-along (CAT) goods, just as in the earlier sections of thispaper.
We denote firm j’s marginal cost of producing variety i in-house by c(j, i). In-house production exhibits constant returns to scale within each variety, but diseconomies of scope acrossvarieties, so that c(j, i) is (strictly) increasing in i.26 We assume moreover that c(j, i) is strictlyincreasing in j; that is, firms indexed j closest to zero are the most productive, and thus havethe lowest marginal cost of production for any given scope. Finally, we assume for convenienceand with little loss of generality that the cost function is continuously differentiable in eachargument. To summarize our assumptions over the in-house cost structure, we have: ∂c(j,i)> 0,∂i∂c(j,i)> 0, and c(·) ∈ C 1 .
∂j

The technology for sourcing goods from arms-length suppliers is deliberately simple in thebaseline version of the model.27 We begin with the assumption of constant returns to both scaleand scope in sourcing, so that the marginal cost to firm j of sourcing a given variety i is simplyĉ(j, i) = ĉ ∀i, j. Together, the assumptions of constant returns to scope in sourcing and decreasing returns to scope in production ensure a simple characterization of firms’ make-or-source
decisions.28 In the next section, we consider firm-level heterogeneity in sourcing technology as
well as the possibly of fixed costs to engaging in Carry-Along Trade.
Finally, all firms face a variety-specific per-unit distribution cost, δ(i), which is independent of
whether a good is made in-house or sourced from an arms-length supplier; constant with respect
to quantity within a variety; identical across firms; and additive with the direct (constant)marginal cost of producing or sourcing the product. Most importantly, the distribution cost
increases with a variety’s distance from the firm’s core product so that δ 0 (i) > 0.29 By design, δ(i)has no influence on the pattern of firms’ make-or-source decisions; from a modeling perspective,
the role of δ(·) is simply to ensure existence of a unique interior equilibrium, so that firms do
25
Thus, the assumptions of the model implicitly rule out ‘mixed CAT’ – the potential that for the same variety,a firm would simultaneously produce in-house and source from an upstream supplier.
26
It is worth emphasizing that we are assuming that the unit cost of production increases for only the marginal
variety as scope expands; our approach is thus consistent with Eckel and Neary (2010).
27
This basic sourcing technology acts much like a wholesaling technology for the firm.
28
Although we find constant returns in sourcing to be the most plausible starting point, we readily acknowledge
the alternatives. Incorporating diminishing returns to scope in sourcing technology is straightforward as long as
the implied ranking of in-house and sourcing cost functions does not change more than once over the supportof possible varieties. Tractability requires only that there exists a unique make-or-source threshold below which
all products will be made in-house and above which additional varieties are CAT products. Our assumption of
constant returns to scope in sourcing is sufficient, but not necessary. Economies of scope in sourcing are more
problematic from a tractability standpoint.
29
Our assumptions over the cost structure for production and sourcing already ensure that firms will offer the
goods closest to i = 0; thus, the sum of direct production (or sourcing) cost and distribution cost is strictlyincreasing in i.

17

Carry-Along Tradenot expand scope infinitely.30 Later, we allow δ(·) to vary by firm as well as variety.
Consumers. A mass of identical consumers (or equivalently downstream assemblers), havenon-degenerate preferences over differentiated goods, where goods are both firm (j) and variety(i) specific. Consumers care only about the firm-variety pair, and (crucially) do not differentiate
between goods produced in-house versus sourced from a supplier. For parsimony, we assume thatany demand-side income effects are absorbed in total market quantity, Q, which is taken as given
by atomistic firms, and that aggregate demand systems are twice continuously differentiable in
relevant arguments.31
In the baseline version of the model, we restrict attention to preference structures thatgenerate (any) demand system in which inverse aggregate demand for product ji may be written
as a function of aggregate parameters (taken as given by the atomistic firms and hereafter
suppressed) and own (aggregate) quantity only:pji ≡ p(qji , Q, ...) = p(qji ) ∀i, j,
but is otherwise independent of firm or variety specific components. Later, we consider alternative preference structures that permit firm-level demand-side spillovers across goods – including
the intra-firm “cannibalistic” demand developed by Eckel and Neary (2010).

7

Firm Behavior and Selection

As discussed earlier, we follow Mrazova and Neary (2011), in presupposing the existence of aunique general equilibrium, so that we may jump immediately to the key equilibrium prediction:
the pattern of firm selection into regular and Carry-Along Trade activities.32 In equilibrium,
each firm makes three decisions (1) entry: whether to enter the market or not, (2) product scope:
how many products, and how much of each and at what price, to sell to the market, and (3)make-or-source: which products to make in-house and which to source from upstream suppliers
via the CAT technology. We consider each decision in turn, beginning with the last.
Make-or-Source Decision.

As outlined earlier, for each variety i it sells, a given firm jdecides whether to produce in-house at constant marginal cost c(j, i), or to access a “fishing”
technology, by which firm j is matched with a supplier from whom to source carry-along products
at constant marginal cost ĉ. Recall that consumers make no distinction between in-house produced goods and CAT goods, distribution costs are similarly independent of the make-or-source
30

Note that equilibrium may exist absent such an increasing marginal cost of distribution – for instance, withthe “quantity cannibalistic” preferences outlined below – but is not guaranteed.
31
We could of course silence income effects by assuming a quasi-linear demand structure with a numeraire good,
but it is not necessary to make such a functional form restriction; see Neary (2009).
32
We address the conditions for equilibrium existence and uniqueness in the appendix.

18

Carry-Along Tradedecision, and (by assumption) the production and sourcing cost structures are independent of
total product scope. The make-or-source decision is therefore simply that which minimizes themarginal cost of any given variety i.33 Given that in-house production exhibits decreasing returns to scope, while the sourcing technology has constant returns to scope, it is immediate thatevery firm will have a unique make-or-source threshold that delineates regular goods from CAT
goods. This threshold, which we denote by k̂(j), is defined implicitly by:c(j, k̂(j)) = ĉ.

(4)Lemma 1 In equilibrium, each firm j will produce in-house all goods i ≤ k̂(j), and will source
the balance (i > k̂(j)) from arms-length suppliers.
For products closest to a firm j’s core production competency (i ≤ k̂(j)), the firm has an in-house
cost advantage relative to the pool of homogeneous arms-length suppliers; for more peripheral
varieties further afield of firm j’s core competency, the marginal cost of in-house production rises,
eventually reaching a point at which the marginal cost of buying from an arms-length supplieris less than the cost of producing in-house.34 The optimal cost function for each firm-productpair may then be written c̃(j, i) ≡ min{c(j, i), ĉ}, and it is simply the lower envelope of the
in-house and CAT-sourced cost curves over the support of varieties. Notice that this minimized
cost function is strictly increasing in i until i ≥ k̂(j) and constant thereafter as shown in Panel
A of Figure 3.
Optimal Scope.

From here, we can define the profit function for any given firm-productpair:
π̃(j, i) = max[p(qji ) − c̃(j, i) − δ(i)]qji .
qji

(5)

Notice three important points: first, the firm-product profit function already embodies the
optimal make-or-source decision, k̂(j), through c̃(·); second, in this simple baseline version of
the model, a firm’s profit function for each variety is independent of the total set of varieties
offered by the firm; third, given the symmetric demand structure and decreasing returns to< 0. Thus,
product “remoteness” (i.e. that c̃(j, i) + δ(i) is strictly increasing with i), ∂ π̃(j,i)∂iwe can summarize a firm’s decision over the set of varieties to sell as the firm’s optimal scopedecision, k – the firm will sell all varieties closest to the core: i ≤ k – and no others.
33
Conversely, the make-or-source decision generally would depend on the equilibrium product scope if thesourcing technology exhibits either economies or diseconomies of scope, or if there is a fixed cost to Carry-Along
Trade and any form of spillovers across goods.
34
It is of course entirely possible to adopt functional form or distributional assumptions such that there exist
firms for which even the core variety is more expensive to produce in-house than to source – we would interpretthese firms as ‘pure’ wholesalers. This said, there are no ‘pure’ wholesalers in our sample (by definition, the data
are for firms that have some production), and so we do not focus on them here.

19

Carry-Along Trade

Figure 3: Firm j’s Optimal Make-or-Source Decision for Each Variety i

20Carry-Along Trade

Aggregating a firm’s profit function for each variety over all offered varieties i ∈ [0, k], firm
j’s total return as a function of scope and productivity is then:Z kΠ(j, k) ≡π̃(j, i)di.

(6)0Taking the derivative with respect to k yields the first order condition that defines implicitly
the firm’s optimal scope, k(j). In the baseline version, this first order condition is remarkably
simple because both the make-or-source decision and the demand functions for each variety are
independent of the total product scope. The firm will optimally continue adding varieties until
the last variety added yields zero profit.35 The FOC is simply:∂Π(j, k)
=
∂k

Z k
|0

∂ π̃(j, i)
di +π̃(j, k) = π̃(j, k(j)) = 0.
∂k
{z
}

(7)

=0

The second order condition is then just that the profitability of the marginal (k th ) variety isdecreasing as scope rises – i.e. that there are diseconomies of scope:∂ π̃(j, k)∂ π̃(j, i)∂c̃(j, i)∂ 2 Π(j, k)o0=== −qji+ δ (i)
< 0.
∂k 2
∂k
∂i
i=k
| ∂i {z
} i=k

(8)

+

The importance of assuming δ 0 (i) > 0 is immediately evident – without it, there is no reason
that an interior equilibrium necessarily should exist for a firm engaged in CAT at the margin:
in this baseline version of the model, demand exhibits no within-firm crowd out (e.g. brandcannibalization), and there are no other supply-side diseconomies of scope once the firm switches
to CAT production (i.e. ∂ĉ
∂i = 0.)Panels A and B in Figure 3 illustrate. For any given variety i, firm j can choose between
producing in-house at constant marginal cost c(i, j) or sourcing a carry-along product from an
upstream supplier at cost ĉ. At k̂(j) the two costs are equal, as shown in Panel A. Below thisthreshold, the cost is lower (and profit is higher) via regular production; above it, marginal cost islower and profit is greater via Carry-Along Trade. In the figure, we label the (hypothetical) firmvariety profit function from regular production by πREG (i, j), while the CAT profit function isdenoted by πCAT (i, j).36 The firm’s profit function given the optimal make-or-source decision,π̃(j, i), is then simply the upper envelope of the two potential profit functions under either
35

Note that with CES preferences, which imply an infinite choke price, one must incorporate a (potentially verysmall) fixed cost for adding each new variety in order to ensure existence of finite k(j). See the theory appendix.
36
Where πREG (i, j) ≡ maxqji [p(qji ) − c(j, i) − δ(i)]qji and πCAT (i, j) ≡ maxqji [p(qji ) − ĉ − δ(i)]qji . Note that
πREG (i, j) is necessarily steeper than πCAT (i, j) for all i ≤ k̂(j) as drawn: regular production exhibits diseconomies∂πREG (j,i)=
of scope∂i in production
 and distribution, whereas CAT has diseconomies only in distribution.

REG
−qji

∂c(j,i)+ δ 0 (i)
∂i

(j,i)
CAT 0
REG
CAT
< ∂πCAT= −qjiδ (i) < 0, given that ∀i ≤ k̂(j), qji
≥ qji
> 0.
∂i

21

Carry-Along Tradeprovisioning strategy, producing in-house (πREG ) or sourcing from an upstream supplier (πCAT ).
In this baseline version of the model, the firm will continue to add varieties until the profit of
the marginal product is zero – i.e. π̃(j, i) = 0 at k(j) – as indicated by the first order conditionin (7).37
Entry. Firms will enter a market if their realized profit is sufficient to cover an exogenous,
homogeneous fixed cost of entry, F . There is no firm-level idiosyncratic component to profit
apart from firm productivity, so only sufficiently productive firms will enter the market. Defining
each firm’s total profit to be the sum of returns to each variety given the optimal scope, Π̃(j) ≡R k(j)π̃(j, i)di, the least productive firm to enter the market, firm j̄, is given implicitly by Π̃(j̄) =0F.
Finally, a note on terminology: in the model, equilibrium product scope is equivalent to
the mass of varieties supplied to the market by a firm. In equilibrium, firm j sells a massof regular varieties, k̂(j) (the range i ∈ [0, k̂(j)]), to the market, with a total variety mass ofk(j) (the range i ∈ [0, k(j)]). The mass of varieties sold via Carry-Along Trade is then simply
max{0, k(j) − k̂(j)} (with range i ∈ (k̂(j), k(j))). This said, we typically refer to product scope– rather than mass of varieties – to avoid potential confusion with quantities of each productsold (the scale of the qji s). When we take our predictions to the data, we interpret productscope as the (discrete) number of varieties supplied to the market.

7.1

Productivity, Regular Products, and Carry-Along Trade

The baseline model’s predictions for the relationship between firm productivity, regular productscope, CAT scope, and (total) product scope follow directly. In characterizing the relationshipbetween firm productivity and the extent of regular and Carry-Along Trade across firms, we
adopt the terminology in Mrazova and Neary (2011), referring to complementarity between
underlying firm productivity and firm activity in a firm’s payoff function as super-modular andnegative complementarity as sub-modular.38
Productivity and Regular Product Scope. Regular product scope is increasing in firm
productivity. Given that the most productive (lowest j) firms have the lowest marginal cost of37

Returning briefly to the potential for diseconomies of scope in sourcing, Panels A and B demonstrate respectively that diseconomies of scope in sourcing (upward sloping ĉ(·) in Panel A) are easily embedded in our model
as long as (i) the ĉ(·) function crosses the in-house cost function c(·) at most once and from above in Panel A; sothat (ii) πREG (·) crosses πCAT at most once from above in Panel B.
38
Formally, a function f : Rn → R is super-modular if ∀~x, ~y ∈ Rn , f (~x∧~y ) + f (~x ∨~~y) ≥ f (~x) + f (~y ), where~x ∧ ~y (~x ∨ ~y ) denotes the component wise minimum (maximum) of ~x and ~
y . When f (~z) is differentiable, as in our∂ 2 f (~z)≥ 0 ∀z1 6= z2 , by Topkis’ Characterization Theorem. (Topkis
framework, super-modularity is equivalent to ∂z
1 ∂z2(1998))

22

Carry-Along Tradein-house production for any given variety i, while the marginal cost of carry-along products is
identical and constant across firms and varieties, it is immediate that the least productive firms(highest j) will be the first to switch from producing in-house to sourcing via CAT:
Lemma 2 k̂(j) is strictly decreasing in j.
Proof. From the implicit definition of k̂(j) in (4) and the implicit function theorem: k̂ 0 (j) =∂c(j,i)∂j< 0. − ∂c(j,i)∂i

Productivity and (total) Product Scope. Optimal (total) product scope is also increasing with firm productivity, but weakly. Among regular-only firms (meaning they produce
everything in-house (i.e. k̂(j) ≥ k(j))), the profit of the marginal product scope variety, k(j),is strictly increasing with firm productivity (decreasing in j) as one would expect given thatthe marginal cost of production for any given variety scope is increasing with j. But forfirms engaged in Carry-Along Trade at the margin, π̃(j, i) = π̃CAT (i), so that the profit of
the marginal product is independent of j. For any given i, all carry-along firms of any productivity face the same demand and symmetric costs of bringing the good to market. Thatis, π̃CAT (i) = maxqji (p(qji ) − ĉ − δ(i))qji . Thus, the equilibrium (total) product scope will be
the same for all firms engaged in Carry-Along Trade, regardless of their initial productivity.
Formally:
Lemma 3 k(j) is weakly decreasing in j.
(i) For regular-only firms (∀j s.t. k̂(j) ≥ k(j)): total product scope is strictly increasing withfirm productivity: k 0 (j) < 0.
(ii) For firms that engage in CAT (∀j s.t k̂(j) < k(j)), total product scope is independent offirm productivity: k(j) ≡ kCAT and thus k 0 (j) = 0.
Proof. From the implicit definition of k(j) in (7) and the envelope condition for (5): k 0 (j) =−∂ π̃(i,j)∂j∂ π̃(i,j)∂j∂ c̃(i,j)

i=k= − ∂ c̃(i,j)∂j∂i+δ 0 (i) i=k. For regular-only firms, the marginal product k is produced in∂c(i,j)

house, so that c̃(j, i = k) = c(j, k), and thus k 0 (j) = − ∂c(i,j)∂j∂i+δ 0 (i) i=k< 0. For CAT firms, thek th variety is sourced from arm-length upstream suppliers at constant marginal cost ĉ, and so
k 0 (j) = − δ00(i) i=k = 0. 
Productivity and CAT Scope. Comparing two firms with differing core productivities,
the more productive (lower j) firm will produce a greater range of products in-house, and thus
necessarily will supply fewer products via Carry-Along Trade. The fundamental mechanism is23

Carry-Along Trade

simple: if firms have the same access to an identical, constant Carry-Along Trade ‘technology’,
then the firms with a lower opportunity cost of sourcing via CAT will use it the most. The mostproductive firms have the least to gain from Carry-Along Trade relative to in-house production,and thus will use it the least.39

Figure 4: High (A) versus Low (B) Productivity Firms
Figure 4 illustrates the relationship between firm productivity and regular, CAT, and (total)
product scope in equilibrium. Firm A has greater core efficiency (jA < jB ) and thus greater
profits for any given regular product i than Firm B. This means that Firm A will find it profitableto produce a greater range of products in-house than Firm B, so that Firm A’s regular productscope is greater than Firm B’s: k̂(jA ) > k̂(jB ). However, since both firms have identical sourcing
technologies, their marginal profit from any given CAT product i > k̂(jA ) > k̂(jB ) will be thesame. As such if both firms engage in any CAT activity, they will have the same optimal total
product scope: k(jA ) = k(jB ). CAT product scope is then necessarily smaller for the moreproductive firm, k(jA ) − k̂(jA ) < k(jB ) − k̂(jB ).
Formalizing the central results of the baseline model yields the following key predictions:39

To rule out infinite entry of wholesalers, we implicitly assume that a CAT-only firm (one that produces
Rk
nothing in-house) cannot cover the (homogeneous) fixed cost of entry, F ; i.e. we assume F > 0 CAT πCAT (i)di.

24

Carry-Along Trade

Proposition 1 For the baseline model in which firms have equal access to a constant ‘sourcing’technology for acquiring carry-along products from arms-length upstream suppliers and demand
is symmetric and independent across firms and varieties:
i Regular product scope, k̂(j), is increasing in productivity; i.e. firm productivity and regularscope are super-modular in firm payoffs;
ii Total product scope, k(j), is identical for all firms engaged in carry-along-trade; i.e. firm
productivity and total product scope are modular in firm payoffs for Carry-Along Traders(for whom k̂(j) ≤ k(j)).
iii Carry-along product scope, k(j) − k̂(j), is decreasing in firm productivity; i.e. firm productivity and Carry-Along Trade are sub-modular in firm payoffs.
Proof. Parts (i) and (ii) follow directly from lemmas 2 and 3 respectively. Part (iii) follows
from (i) and (ii).
Extending the results to include predictions for not just product scope – the number (technically mass, given the theory’s continuum setting40 ) of varieties supplied to the market embodiedo s), generates
in k̂ and k – but also scale – how much of each product is sold in equilibrium (the qji

the following additional predictions:
Corollary 1.1 In the baseline model, sales volumes will be uniformly higher for regular products
than for carry-along varieties. Within regular products, sales volumes will be highest for the mostproductive firms, and for products closest to a firm’s core variety. Carry-along product volumes
will be highest for products closest to a firms’ core variety, but otherwise independent of firm
productivity.
o is inversely related to varietyProof. Given symmetric demand, the within-variety scale, qji

specific marginal cost of provisioning, but otherwise symmetric across firms. c̃(j, i) + δ(i) is
by definition lower for all regular products than for CAT products (within a given firm), andhigher for less productive firms (for any given variety). Within regular products, diseconomies
of scope arise in both direct production cost and distribution, whereas only the distribution cost
component obtains for CAT products. The predictions encompassed in Proposition 1 and Corollary 1.1 are the opposite of what
we observe in the data. From Table 7 and Figure 2 presented earlier, the number of carry-alongproducts is positively correlated with firm productivity, and it is the most productive firms, not40

As in Bernard et al. (2011), we interpret the HS6+ codes as discrete partitions of the model’s continuum of
products.

25

Carry-Along Tradethe least, that do the most carry-along trading in both volume and scope. We do see regular
product volumes and regular product scope are highest for the most productive firms, but wealso observe a positive correlation between CAT product volumes and firm productivity. (We donot, of course, have a reasonable measure of a product’s distance from a firm’s core productivity,
so we have little to say on that dimension.)
Given that the baseline version of the model is unable to rationalize the patterns in the data,
we now turn to more complicated modeling structures. Before doing so, however, it is worthwhile to restate the key features of the data, and hence the central predictions that a plausiblemodel must generate. First, regular (in-house) product scope and volumes increase with firm
productivity. Second, CAT product scope and volumes also increase with firm productivity.
Third, CAT product scope is more responsive to firm productivity than regular product scope.
The baseline model can deliver only the first of these three patterns in the data. A variety ofpotential modeling structures can deliver all three of these predictions given sufficiently nuanced
assumptions, but as we discuss below, they differ in plausibility and generality.

8

Alternative Modeling Frameworks

Fundamentally, any model that rationalizes the data must have sufficient super-modularity infirm payoffs between total product scope, k, and firm productivity, j. From the data, we knowthat more productive firms sell the broadest range of both regular and CAT products. And
because regular (in-house) production and carry-along sourcing are substitute activities for any
given variety (products that are made are not carried along, and vice versa), it therefore must
be the case that the total number of varieties (i.e. total product scope) increases faster with firm
productivity than does the number of regular products (regular product scope). Total productscope, k and firm productivity must be more super-modular in firm payoffs than are regular
product scope, k̂ and firm productivity.

8.1

Alternative Supply Side

We consider three plausible extensions to the supply-side set-up in the baseline model. The
first allows firm-level heterogeneity in the CAT sourcing technology. The second maintains theassumption of identical CAT technology as in the baseline model, but introduces a fixed cost
to Carry-Along Trade. Finally, we consider the possibility that more efficient producers also
have more efficient distribution networks. We work through these extensions quickly with the
expectation that the reader is now familiar with the basic framework and central mechanisms.

26

Carry-Along Trade

8.1.1

Heterogeneous CAT Technology

We maintain the assumption of constant returns to scale in CAT sourcing technology bothwithin and across varieties, but we now let the cost of output sourced from upstream suppliers
vary across firms according to ĉ(j). It is obvious that the only way for the model to predict
super-modularity between CAT scope and productivity is for the firm-level CAT cost, ĉ(j) tobe monotonically (and sufficiently) increasing in j, so that the most productive firms also haveaccess to the lowest cost upstream suppliers; thus, we assume that ĉ0 (j) > 0.41
The equilibrium make-or-source threshold, k̂(j), is now defined implicitly by c(j, k̂(j)) = ĉ(j),and the minimized cost function is c̃(j, i) ≡ min{c(j, i), ĉ(j)}; it is still the lower envelope of the
in-house and CAT-sourced cost curves. The only difference is that the “kink” at k̂(j) may occur
earlier or later for firms with different productivity, since both the regular and CAT cost curves
shift down for higher productivity firms. (Lemma 2 no longer obtains; we cannot state withany certainty the ranking of k̂(j) across firms.) At the same time, total product scope is now
monotonically increasing with firm-level productivity, even for firms engaged in Carry-Along
Trade; i.e. k 0 (j) < 0,42 (Lemma 3 (ii) no longer obtains.)
The model can deliver predictions consistent with the data, but need not. Indeed, the key
features exhibited by the data are something of a special case, or “Goldilocks” result for themodel: if a firm’s access to superior carry-along technology is too highly correlated with its core
in-house productivity, then regular product scope k̂(j) will be decreasing in firm productivity.
Conversely, if the carry-along technology is insufficiently correlated with in-house productivity,
then carry-along scope will continue to be negatively related to productivity in equilibrium.
Only if carry-along sourcing technology and core firm productivity are just right, sufficiently
correlated but not too correlated, can the model generate the prediction that both regular andcarry-along product scope increase with firm productivity.
The three panels in Figure 5 illustrate. Each compares a more productive Firm A with aless productive Firm B (i.e. jA < jB ). In Panel A, carry-along technology is increasing too
quickly with firm productivity, so that regular scope is sub-modular with firm core productivity.
Panel B depicts the opposite extreme in which ĉ(j) increases too slowly as j rises, so thatCAT scope continues to be sub-modular with productivity, as in the baseline model. Panel C
41
For simplicity, we simply assume the relationship between sourcing technology and underlying firm productivity here, but richer micro-foundations are certainly possible. One particularly intriguing possibility consistent
with ex-post heterogeneous sourcing technology under incomplete contracts is along the lines of Grossman andHart (1986): if more productive firms have (endogenously) superior bargaining power with potential upstream
suppliers, they will have ex-post lower sourcing costs. (We thank Gordon Hanson for pointing out this potential
mechanism.)
2
(j,k)
42
Note the super-modularity between productivity (lower j) and scope: Π∂k∂j= ∂π(j,i)=∂ji=k<k̂(j)− ∂ c̃(j,i)= − ∂ ĉ(j)
< 0.
∂j
∂j
i=k

27

Carry-Along Trade

Figure 5: Heterogeneous Sourcing Productivity
28

Carry-Along Tradeillustrates the intermediate scenario in which ĉ(j) and c(j, i) vary with j in such a way as tomatch the regularities we have identified in the data. While the introduction of heterogeneous
sourcing costs that are positively correlated with production costs can reconcile the model withthe three main stylized facts, the “Goldilocks” nature of the resulting equilibrium is somewhat
unappealing.43
8.1.2

Fixed Costs to engaging in Carry-Along Trade

Another initially appealing explanation lies in fixed costs. It seems somewhat intuitive that
more productive firms would earn higher profit in their regular production, and thus will bebetter positioned to leverage themselves into carry-along activities. To the contrary, we findthat introducing a fixed cost to engaging in Carry-Along Trade offers even less traction forrationalizing the data.
Suppose we introduce a homogeneous fixed cost to Carry-Along Trade, Ω, but maintainthe remaining features of the baseline model (including homogeneous, constant marginal costof carry-along goods). Any firm that would earn sufficient profit over its CAT products,
R k(j)
Π̃CAT (j) ≡πCAT (i)di ≥ Ω, would pay the fixed cost of entering the carry-along market.
k̂(j)From Proposition 1, however, we know that among firms that engage in Carry-Along Trade,the most productive firms do the least CAT in favor of in-house production. Thus, only thelower productivity firms would do enough Carry-Along Trade to justify the fixed cost Ω; higher
productivity firms with a lower cost of in-house production would instead substitute away from
CAT in favor of regular products. Figure 6 illustrates. Notice that the total return to firm jfrom carry-along products is the area under the per-product profit function π̃(j, i) for the setof sourced varieties, i ∈ [k̂(j), k(j)]. For any pair of firms A and B where A is relatively moreproductive (i.e. jA < jB ), we have that
Z k(jA )Π̃CAT (jA ) ≡Z k(jB )πCAT (i)di < Π̃CAT (jB ) ≡k̂(jA )πCAT (i)di.
k̂(jB )The introduction of fixed costs of CAT to the baseline model thus serves only to increase
the disconnect with the data. Rather than rationalizing our empirical finding that the mostproductive firms both produce and source more products, the fixed cost extension of the model
implies that the least efficient producers have an even greater incentive to source products thanin the baseline model.
43

Moreover, the heterogeneous sourcing cost explanation becomes even more difficult to reconcile with the data
once we consider that not only is the number of CAT products positively related to firm productivity, but also theshare of CAT products in total number of exported products is increasing with firm productivity; in essence, thebroad knife edge result becomes yet narrower given the additional stylized fact seen in the CAT product shares.

29

Carry-Along Trade

Figure 6: Fixed Costs of Carry-Along Trade
8.1.3

Heterogeneous Distribution Technology

Another potential explanation lies in differential distribution costs. More efficient producers
may also be able to more easily create distribution networks. We maintain the assumption of
constant returns to scale in CAT sourcing technology both within and across varieties, but wenow let the distribution function, δ(j, i), vary across firms such that ∂δ(j,i)> 0, ∂δ(j,i)
> 0.
∂i
∂j
Since the distribution cost does not depend on whether the product is produced or sourced, it
will not affect the make-or-source choice of the firm. More efficient producers will make a wider
range of products as in the baseline model and regular products will be super-modular in firm
productivity. Total firm scope will now be increasing in firm efficiency as the most productive
firms face lower distribution costs at the margin. Once again, the relationship between CAT
scope and firm productivity depends on how rapidly distribution costs fall as firm efficiency
increases. Distribution costs must fall sufficiently rapidly to allow the difference between regular product scope and total product scope (which are both increasing in productivity) to also
increase.
We find the heterogeneous distribution cost explanation to be plausible, though it necessarily
implies that there are two separate dimensions of exogenous firm heterogeneity, core manufacturing productivity and distribution-network acumen, and that these strengths are sufficiently
and positively correlated to generate the patterns observed in the data.

30

Carry-Along Trade

8.2

Alternative Demand Side

We now turn to potential demand-side explanations for the patterns observed in the data.
Throughout this section we continue to assume that preferences are symmetric both acrossvarieties within a firm, and across firms with the same number of varieties. We could relax
this assumption by introducing ex-ante exogenous firm-specific demand components or variety
specific “popularity” draws (as in as in Bernard et al. 2011), but this would add more complexity
at the cost of tractability.
Because preferences are central in the subsequent analysis, we take a moment to delineate
three broad classifications. Each carries important differences for the predicted nature of CAT
behavior across firms. The first class of preferences, independent symmetric, are just what wehave already assumed in the baseline case: any preference structure that generates demand
functions with no firm or variety specific idiosyncratic component. Namely, pji ≡ p(qji ).
We refer to preferences as quantity cannibalistic if they generate demand that depends on afirm’s total quantity of output supplied to the market, so that inverse demand may be written
R k(j)
pji = p(qji , Qj ), where Qj ≡ 0 qji di. Generally, within-firm quantity cannibalization isassumed to be negative (as in Eckel and Neary (2010), Dhingra (2011), and Arkolakis andMuendler (2011)), so that inverse demand satisfies∂p(qji ,Qj )< 0 ∀ji.
∂Qj

Finally, we introduce a third class of preferences, which exhibit what we call demand scopecomplementarity. This new class of preferences exhibits the property that demand for a given
firm’s variety increases as the firm’s total scope of product offerings increases. The idea issimply that ceteris paribus consumers prefer to buy products from firms that offer a wider
range of varieties.44 In this case, inverse demand may be written, pji = p(qji , k(j)) where∂p(qji ,k(j))> 0 ∀ji.
∂kNote that demand complementarity is perfectly compatible with quantity

cannibalistic preferences – that is, we could allow pji = p(qji , k(j), Qj ), where p(·) is increasingin the second argument and decreasing in the first and third arguments. We omit this additional
complication in our discussion below for the sake of parsimony. As mentioned earlier, we rule out
preferences that generate demand structures that otherwise depend on firm or variety-specificcomponents other than total firm scope or output.
8.2.1

Quantity Cannibalistic Preferences

With demand-side spillovers across varieties within a firm, a firm’s optimal scope decision becomes somewhat more complicated. Note, however, that the make-or-source decision remains
unchanged as long as demand-side spillovers remain independent of whether products are made44
For instance, a consumer may like all of his apparel and footwear to display an embroidered swoosh, or adownstream assembler may prefer ‘one stop shopping’ for her intermediate inputs.

31

Carry-Along Tradein-house or supplied by upstream firms as assumed here. In deciding how many varieties to sellto the market, each firm now weighs the direct benefit of the k th product (its own profit, π̃(j, k))against the indirect cost of expanding firm scope (the demand-side spillover cost, DS(j, k), via
within-firm quantity cannibalization). The revised first order condition for optimal firm scopeis:∂Π(j, k)∂k

Z k

∂ π̃(j, i)
di + π̃(j, k)∂k0
Z k∂p(qji , Qj ) ∂Qj o=
q di +π̃(j, k) = 0
∂Qj
∂k ji
0
{z
}
|
=

(9)

demand spillover≡−DS(j,k)≤0=⇒ π̃(j, k) = DS(j, k).
Crucially, the demand-side spillover imposes a larger cost on more productive firms: moreproductive firms have a lower marginal cost of production for any given variety, and thus produce∂qji∂j < 0) . For any given scope, k, the same quantity∂p(qji ,Qj ) ∂Qj
cannibalization demand shift embodied in∂Qj∂k is applied to more units of production
for more productive firms, resulting in a larger negative demand-side spillover.45 Figure 7

a greater quantity of each product (i.e.

illustrates, where again we compare a more productive firm A with a less productive counterpart
B. The demand-side cost of quantity cannibalization is larger for the more productive firm – i.e.
DS(jA , k) > DS(jB , k) ∀jA < jB , k. Moreover, for any given k, the carry-along profit function,
πCAT (i, j) now also depends on j via Qj , again disciplining the productive firm relative to its lessproductive counterpart. It is immediate that total scope is thus decreasing in firm productivity
among the set of firms engaged in any Carry-Along Trade. At the same time, regular scope
and firm productivity remain super-modular, and so carry-along scope must necessarily be submodular in firm productivity.
8.2.2

Demand Scope Complementarity

In the final extension, we consider the potential for positive demand-side spillovers via demandcomplementarity in consumer (or downstream assembler) preferences. As noted earlier, we now
adopt a demand structure so that inverse demand for every variety within the set of a firm’s
product offerings is increasing with its (total) product scope: pji = p(qji , k), where∂p(qji ,k)> 0.
∂kAs before, the make-or-source decision is independent of the total product scope or theextent of demand-side spillovers. Now, however, each firm’s (total) product scope, k, depends
45
If demand is not linear in total quantity, Qj , then of course an additional asymmetry may arise across j via∂p(qji ,Qj ) ∂Qj. The sign of this potential second order effect is ambiguous.
∂Qj
∂j

32

Carry-Along Trade

Figure 7: Intra-firm Quantity Cannibalization
crucially on the extent of demand complementarity. Unsurprisingly, total product scope is now
increasing with firm productivity: because more productive firms sell larger quantities of each∂qof their regular products ceteris paribus ( ∂jji < 0), the demand-side spillover – now positive(a shift up in inverse demand for all of the firm’s varieties) – from adding a k th product isgreater for higher productivity firms. Now note that the demand side spillover cost is actuallya benefit. Figure 8 illustrates a case in which demand complementarity is sufficient to generate
super-modularity between firm productivity and CAT-scope.
One can see this super-modularity between productivity and total product scope in the firm
payoff function more formally by examining the cross partial derivative:∂ 2 Π(j, k)
∂k∂j

Z k
=
0

∂ 2 π(j, i)∂ π̃(j, k)
+
∂k∂j
∂j
| {z }=0∀k≥k̂(j)Z k 2o∂ p(qji , k) o∂p(qji , k)  ∂qji=qji +di < 0∂k∂qij∂k∂j0|{z} |{z}
(−)

(10)

(+)

We now have that both regular product scope and total product scope are super-modular
with productivity in firm payoffs (necessary conditions to rationalize the data, but not yet
sufficient). The sufficient condition for CAT scope and productivity to be super-modular –33

Carry-Along Trade

Figure 8: Demand Complementarityand hence for realized equilibrium CAT product scope to be rising with firm productivity is ofcourse that the total product scope is increasing faster with firm productivity than is regular
product scope for all CAT firms: k 0 (j) < k̂ 0 (j) < 0 for all j s.t. k̂(j) < k(j), in essence, that
(total) product scope and productivity are more super-modular than regular product scope andproductivity.
While demand scope complementarity is an exogenous characteristic of preferences in ourcontext, a similar mechanism – albeit with a very different interpretation – may be found in the
recent work of Eckel, Iacovone, Javorcik, and Neary (2011). In another context, they develop amodel in which multi-product firms endogenously invest in firm (brand) “quality” – effectively afirm-level demand shifter. In their model, the technology for quality innovation is structured insuch a way to induce increasing returns to (quantity) scale. More productive (lower cost) firms,
thus invest more in brand quality, and would, therefore, optimally offer greater product scopein equilibrium, all else equal.46 Thus, their model exhibits a form of ex-post quality-induced
demand complementarity, which has similar equilibrium characteristics to the preference-based
demand-scope complementarity introduced here.
Briefly summarizing the theory, we find that while the baseline model of CAT fails to match
46
More precisely, the model of Eckel et. al (2011) allows both firm- and firm-product level quality investment,
but it is only the firm-level quality adjustment, Z̄ in their model that can lead to a form of induced demandcomplementarity.

34

Carry-Along Tradethe three main features of the data, several relatively straight-forward supply-side and preferencebased extensions can deliver the desired predictions. If more efficient producers also have either
lower sourcing costs (but not too low) or lower distribution costs then they will have greater
regular product scope, CAT product scope and total product scope. On the demand side, if
demand side complementarities are sufficiently strong, then the most productive firms will supply
more regular and CAT products to the market.
As with the heterogeneous distribution cost explanation, we find that demand complementarity must be sufficiently strong to rationalize the patterns observed in the data. In contrast
to the supply-side explanations, however, the demand side complementarity mechanism has theappealing feature that firms continue to differ in only the single dimension of core manufacturing productivity but are in all other ways ex-ante identical and subject to the same demand
structure, distribution costs, and upstream CAT-sourcing technology.

9

Back to the Data

In this section we consider additional implications of the model for the data on regular and CAT
exports. We also summarize interviews conducted with exporting firms in both Belgium andthe U.S. and report the findings of a specific “case” study.
We have shown that both supply-side or demand-side extensions of the basic model canmatch the positive relationship between firm productivity and the numbers of both sourced
and produced products. In each case, the extended model predicts that the total export valueof regular products will be greater than the total export value of CAT products at the firmlevel for all firms. In addition, the export value of both regular and CAT products should be
increasing in firm productivity. The top panel of Figure 9 shows that firm-level regular exports
are indeed larger than CAT exports at all levels of productivity and that both are increasing as
firm productivity rises for manufacturing exporters.
Both extensions also yield predictions for the average export value per product. Averagefirm-product exports should be greater for regular products than for CAT products within thefirm. These differences should increase as firm productivity rises. The bottom panel of Figure
9 confirms that the average exports are greater for regular products than for CAT products
and that the difference increases as firm productivity rises. Although these predictions from thetheory are confirmed in the data, they do not help us understand whether CAT is more likely
to come from supply-side or preference-based extensions to the basic model.
To both confirm the existence of CAT and to help distinguish between the supply-side andpreference-based explanations, we interviewed more than 20 exporting firms in a variety of
sectors in the US and Belgium. Every firm reported exporting products that it did not make35

Carry-Along Trade

Figure 9: Productivity and Total and Average Exports, 2005
(pure CAT) and several firms discussed using outside suppliers to obtain additional quantities
of products that were produced in-house (mixed CAT). Firms were most likely to describe
CAT products as extending the range of products produced in-house to meet customer demand.
However, we also found evidence of supply-based CAT as one firm with a specialized exporting
technology, e.g. frozen food, exported sourced products to fill containers, and another firm
exported locally-sourced customized containers to its foreign subsidiaries.
A simple, fairly typical example of CAT exports comes from a firm we will call “Company
A”. Established more than 200 years ago, Company A is a manufacturing firm in the foodsector which produces in roasted coffee. Since the 1970s the company has specialized in theout-of-home (non-retail) market, supplying coffee, coffee systems and coffee service to offices,36

Carry-Along Trade

hotels, restaurants and events. Company A is a medium-sized company, but is one of the largest
players in its segment in Belgium and a relatively large player in the European Union.47 Coffee
production is centralized in Belgium and the firm exports its coffee to 25 countries, mainly
within the European Union.
In addition to exporting its core product, roasted coffee, Company A exports a wide varietyof additional goods ranging from coffee vending machines, sugar, milk, cookies, tea, soup, plastic
cups and spoons, to kitchenware (e.g. coffee cups). Company A only produces coffee in-house.
The other products are sourced from external suppliers, i.e. these are Carry-Along Trade products. These Carry-Along Trade products are obtained from Belgian or foreign manufacturers,
depending on expedited availability and price. The firm normally only exports Carry-Along
Trade (sourced) products to destinations where they export coffee.
Company A is not selling coffee, but rather is selling a bundle of products for the serviceof the coffee room. A specific characteristic of the out-of-home coffee market is that it is very
important to provide clients with a full service package (the complete coffee room), rather thanjust providing them with coffee. CAT products serve a double purpose for the firm: (1) they
enable the firm to provide clients with a complete coffee room and (2) they are important froma commercial perspective, since the CAT products (e.g. sugar and milk) typically also carry thefirm’s brand name. The coffee room service package tends to be country-specific, depending on
the coffee drinking habits in different countries. For instance, in some countries coffee tends tobe served with cookies, while in other countries cookies are not part of the “coffee experience”.
This bundle is adapted according to the customer’s and country’s specific needs.

9.1

Export Prices and Export Scope

The case study and the company interviews highlight the role of demand-side factors in CarryAlong Trade. We conclude by examining the relationship between firm-product export prices
and the range of products delivered to an individual destination to look for evidence of demandscope complementarities. Recalling that pji = p(qji , k), where∂p(qji ,k)> 0, ceteris paribus we∂kexpect to find that export prices for the same product sent by the same firm will be increasingin the number of products sent to the country. We use the firm-product-country trade data for2005 to test this simple prediction.
Specifically, we estimate a regression of the form
lnPf pc = βScopef c + γlnQf pc + θτpc + dc + df p + εf pc(11)where lnPf pc is the log of the export price by firm f in product p to country c, Scopef c is therange of products exported by the firm to the country (in logs or levels), lnQf pc is the quantity
47

In 2005, Belgium was the fourth largest exporter of roasted coffee (faostat.fao.org).

37

Carry-Along Trade

exported by the firm in the product to the country, τpc is the level of the tariff on product p incountry c, and dc and df p are country and firm-product fixed effects (additional specifications
include product-country fixed effects, dpc ). The theory of demand-scope complementarities
predicts that β should be positive.
An obvious difficulty with the specification in Equation 11 is that any firm-country demand
shifter, such as country-level variation in the taste for the firm’s brand, will be correlated withboth the price in the destination and the number of products supplied to the market. To help
with this problem, we instrument for the number of products supplied by a firm to an individual
country with a measure of firm-destination average tariffs,
avgτf c =

1 X
τf pc
N
p∈Ω

where Ω is the entire set of possible products that could be exported, including all products
produced by the firm in Belgium or exported by the firm to any destination.48 Higher average
tariffs should reduce the number of products shipped to the market but should not directly affectthe price except through the own-tariff, τf pc , which is included in the second stage regression.
Because of our dependence on variation in tariffs across destination markets, our sample only
includes exports outside the European Union. We also construct the dependent variable only for
product categories that are represented by a single HS6 code to avoid problems in calculating
prices for HS6+ bundles.49
Table 9 reports OLS and IV regression results for specifications with Scopef c measured byeither the log or the level of the number of exported products.50 In all cases product scope has
the expected positive and significant sign. Across destinations, the price of a product exportedby the firm is higher when the firms ships a greater number of total products.

10

Conclusion

This paper introduces the concept of Carry-Along Trade (CAT) – the observed phenomenon inwhich firms sell more products to the market than they actually produce – in effect “carrying
along” products from unaffiliated producers to a destination market.

Matching trade andproduction data for a large sample of Belgian manufacturing firms, we show that Carry-Along48

We do not instrument for the quantity as we are interested in controlling for equilibrium quantity but not in
estimating supply or demand elasticities.
49
The number of exported products includes both HS6 and HS6+ products.
50
The first stage regressions are well-behaved as higher average tariffs faced by the firm in the destinations
reduce the number of exported products. The F-stat form the first stage regressions are reported in Table 9,complete results are available upon request. Due to the large number of both firm-product and country-productfixed effects, all specifications are estimated in differences (demeaned) and the standard errors are adjusted
accordingly.

38

Carry-Along Trade

Trade is pervasive across firms and products and accounts for a substantial share of exports.
More than 90 percent of manufacturing exporters ship a product that they do not make andthese products represent 30 percent of export value.
Across firms, we find that Carry-Along Trade plays an important role in shaping the relationship between firms’ exports and firm productivity. Previous work on the extensive margins
of trade has found that more productive firms export more products. This correlation is largely
due to the presence of CAT. The number of exported CAT products is strongly increasing infirm productivity while the number of exported produced products is weakly increasing in firm
productivity.
To explain these empirical regularities, we develop a simple model of heterogeneous, multiproduct producers and sourcing. Producers choose whether to make or source each variety andselect optimal product scope for the firm. The basic framework with heterogeneous marginal
production costs but common marginal sourcing costs across firms cannot match the stylized
facts about Carry-Along Trade. While the scope of produced goods rises with firm productivity
matching the findings from the data, total product scope is invariant to firm productivity amongfirms that do any sourcing and the scope of sourced products falls as firm productivity rises. We
address both supply-side and demand-side extensions to the model. Allowing for sourcing or
distribution costs that are positively correlated with products costs can match the stylized facts
on the number of exported products. On the demand side, we introduce preferences that exhibit
demand-scope complementarity, the demand for a firm-product is increasing in the number of
products delivered to the market. We find empirical support for such preferences in firm-productexport price data across countries.
There are several directions for future research both empirical and theoretical. Our findings
call into question the basic assumptions about the nature of the manufacturing firm and the
product they produce and sell. A richer set of models of multi-product firms with sourcing canhelp in developing our understanding of domestic and global supply chains and how they evolveand respond to policy changes. This paper presents a view of CAT at a point in time but work
is needed to understand how firms develop their portfolio of products delivered to each market,
both produced and sourced, and how these products respond to shocks to profitability. In addition, the presence of sourced products adds yet another complication to the emerging literatureon estimating productivity in multi-product firms (De Loecker et al 2012). A major avenue
for future empirical work is the identification and analysis of the upstream producers (domestic
or foreign) of the CAT products. Empirical research is just beginning on trade between firms
inside countries, e.g. Atalay, Hortacsu and Syverson (2012), but we know of no comprehensive
dataset that matches domestic suppliers of sourced products and the sales of those products at

39

Carry-Along Tradedownstream firms. The development of data that links firms throughout the supply chain is offundamental importance.

40

Carry-Along Trade

References[1] Ahn, J., Khandelwal, A. and Wei, S. (2011). ”The role of intermediaries in facilitating
trade”, Journal of International Economics, 84(1), 73-85.
[2] Akerman, A. (2010). ”A theory on the role of wholesalers in international trade based on
economies of scope”, Research paper in Economics 1, Stockholm University, Department of
Economics.
[3] Arkolakis, Costas and Marc-Andreas Muendler (2011) “The Extensive Margin of Exporting
Goods: A Firm-Level Analysis”, Yale University, mimeograph.
[4] Atalay, Enghin, Ali Hortascu, and Chad Syverson (2012) “Why Do Firms Own Production
Chains?”, NBER Working Paper No. 18020.
[5] Bernard, Andrew B., Marco Grazzi and Chiara Tomasi (2011) “Intermediaries in International Trade: Direct and Indirect Modes of Export”, NBER working paper No. 17711.
[6] Bernard, Andrew B., J. Bradford Jensen, Stephen J. Redding and Peter K. Schott (2007)“Firms in International Trade,” Journal of Economic Perspectives, 21(3), 105-130.
[7] Bernard, Andrew B., J. Bradford Jensen, Stephen J. Redding and Peter K. Schott (2010)“Wholesalers and Retailers in US Trade,” American Economic Review, Papers and Proceedings, 100(2), 408-413.
[8] Bernard, Andrew B., Stephen J. Redding and Peter K. Schott (2009) “Products and Productivity,”Scandinavian Journal of Economics, 111(4) 681-709.
[9] Bernard, Andrew B., Stephen J. Redding and Peter K. Schott (2011) “Multi-Product Firms
and Trade Liberalization,” Quarterly Journal of Economics, 126(3), 1271-1318.
[10] BvDEP (2006) Belfirst Database (Brussels: Bureau Van Dijk Electronic Publishing).
[11] Caves, Douglas W., Laurits R. Christensen and W. Erwin Diewert (1982) “The Economic
Theory of Index Numbers and the Measurement of Input, Output and Productivity,” Econometrica, 50(6), 1393-1414.
[12] Eckel, Carsten, Leonardo Iacovone, Beata Javorcik, and J. Peter Neary (2011) “Multiproduct Firms at Home and Away: Cost- Versus Quality-Based Competence,” CEPR
Working Paper 8186 (January).

41

Carry-Along Trade[13] Eckel, Carsten and J. Peter Neary (2010) “Multi-product Firms and Flexible Manufacturingin the Global Economy,” Review of Economic Studies, 77:1, January, 188-217.
[14] De Loecker, Jan, (2011) “Product Differentiation, Multi-Product Firms and Estimating the
Impact of Trade Liberalization on Productivity”, Econometrica, Vol. 79, No. 5 (September),
1407-1451[15] De Loecker, Jan, Pinelopi K. Goldberg, Amit K. Khandelwal, and Nina Pavcnik, (2012)“Prices, markups and Trade Reform”, NBER Working Paper No. 17925.
[16] Dhingra, Swati (2011) ”Trading Away Wide Brands for Cheap Brands” LSE mimeo.
[17] Eurostat (2006) Prodcom: Statistics on the Production of Manufactured Goods (Luxemburg: Eurostat).
[18] Foster, Lucia, John Haltiwanger, and Chad Syverson (2008) “Reallocation, Firm Turnover,and Efficiency: Selection on Productivity or Profitability?” American Economic Review,98(1): 394-425.
[19] Goldberg, Pinelopi K., Amit Khandelwal, Nina Pavcnik and Petia Topalova (2010) “Multiproduct Firms and Product Turnover in the Developing World: Evidence from India,”
Review of Economics and Statistics, 92(4), 1042-1049.
[20] Grossman, Sanford J., Oliver D. Hart (1986) “The Costs and Benefits of Ownership: A
Theory of Vertical and Lateral Integration,” Journal of Political Economy, 94(4), 691–719.
[21] Iacovone, Leonardo and Beata S. Javorcik (2010) “Multi-product Exporters: Product
Churning, Uncertainty and Export Discoveries,” Economic Journal, 120, 481-499.
[22] Mayer, Thierry, Marc J. Melitz and Gianmarco I. P. Ottaviano (2011) “Market Size, Competition and the Product Mix of Exporters,” Harvard University, mimeograph.
[23] Mayer, Thierry, and Gianmarco I. P. Ottaviano (2008),” The Happy Few: the Internationalisation of European Firms”, Intereconomics, May/June, 135-148.
[24] Mrazova, Monika, and J. Peter Neary (2011), ”Selection Effects with Hetergeneous Firms”,
Oxford University mimeo.
[25] Neary, J. Peter (2009). “International trade in general oligopolistic equilibrium,” Oxford
University mimeo.
[26] Petropoulou, D. (2007). ”Information costs, networks and intermediation in international
trade”, Economics series working papers, University of Oxford, Department of Economics.
42

Carry-Along Trade[27] Rauch, J. E. (2001) ”Business and Social Networks in International Trade”,Journal of
Economic Literature 39 (December): 1177-1203.
[28] Rauch, J. E. and Watson, J. (2004). ”Network intermediaries in international trade, Journalof Economics” & Management Strategy 13(1): 69–93[29] Topkis, Donald M. (1998), Supermodularity and Complementarity, Princeton University
Press, Princeton, NJ.
[30] Van Beveren, Ilke, Andrew B. Bernard and Hylke Vandenbussche. (2012), ”Concording EU
Trade and Production Data over Time” Tuck School of Business mimeo.

43

Carry-Along Trade

Theory Appendix
Here we briefly address the conditions for industry equilibrium existence and uniqueness. Industry equilibrium is characterized by (i) the set of active firms, (ii) the set of products producedby each firm, and (iii) the equilibrium price and quantity for each (firm specific) product soldto the market; together, (i) − (iii) determine the (fixed point) equilibrium aggregate industry
output, Q.

Baseline Caseo (Q), po (Q)) for any (firm specific)
Beginning with (iii), the equilibrium price-quantity pair (qjijiproduct ji is simply that which maximizes firm j 0 s profit. In the baseline case in which there areno supply or demand side spillovers across products within the firm, the profit maximizing priceand quantity choices are independent across products within (and across) firms. As a functionof aggregate quantity (recall, taken as given by atomistic firms):oqji(Q) = arg max p(qji , Q) − c̃(j, i) − δ(i, j),
qji

(12)

which is unique under our assumptions of (strictly) downward sloping own-demand ∂p(·)∂qji < 0and constant returns to scale within product dc(j,i)
dqji = 0 ∀qji . Existence requires that there exists
some positive, finite q̂ji s.t. p0 (q̂ji , Q)q̂ji + p(q̂ji , Q) ≤ c̃(j, i) + δ(i, j). The equilibrium price iso , Q).
then given by inverse demand, s.t. poji (Q) ≡ p(qjiOptimal scope (ii): Given the existence of a unique profit maximizing price-quantity pairfor every firm-variety product ji given Q, the equilibrium scope of varieties k(j; Q) produced byany given firm j is defined implicitly by the first order condition in (7):∂Π(j, k)
∂k

Z k
=
0

|

∂ π̃(j, i)
di +π̃(j, k) = π̃(j, k) = 0.
∂k
{z
}

(13)

=0

Uniqueness of the optimal scope decision for each firm j is ensured by the second order condition in (8), which holds with strict inequality under our assumption that δ 0 (i) > 0. An
interior optimal scope decision k(j, Q) exists as long as there exists some finite scope î such thatπ̃(j, î; Q) ≤ 0∀j. (Note that with CES preferences, one needs to assume some strictly positive
fixed cost to producing each variety to ensure that firms do not expand scope infinitely. Such afixed cost would complicate exposition but otherwise would not qualitatively change the resultsof our general model.)Entry of firms (i): Firms enter as long as total returns (from all produced varieties) cover
the fixed cost of entry, F . The set of firms in the market is the set Ω(Q) ≡ [0, j̄(Q)] where44Carry-Along Tradej̄(Q) – the least productive firm to enter the market – is given implicitly by Π̃(j̄(Q)) = F where
R k(j)
Π̃(j, Q) ≡ 0 π̃(j, i; Q)di. Uniqueness and existence of j̄(Q) are ensured by our assumptions
that ∂c(j,i)< 0 and sufficiently large F to exclude wholesalers.
∂jAggregate equilibrium quantity Q is then simply the fixed point solution to (i) − (iii)
R j̄(Q) R k(j;Q) oqji (Q)didj.
00o (Q), po (Q) ∀j ∈ Ω(Q), i ≤ k(j; Q) , where Q ≡qjijiGeneral Conditions
The general case analog for (12) explicitly recognizes potential within brand spillovers:51oqji(Q) = arg max p(qji , Q) − c̃(j, i) − δ(i, j) +qjiZπjh (j, h; Q, qji )dh,

(14)

/i

Uniqueness of qji o (Q) and pji o (Q) is again implied by downward sloping demand and constantreturns to scale in production, sourcing, and distribution as long as intra-firm spillovers are notboth large and positive (i.e. positive quantity cannibalization, which we do not consider). As inthe baseline case, existence requires the existence of some positive finite q̂ji such that marginal
revenue is less than marginal cost, net of intra-firm spillovers.
The general first order condition for optimal scope includes any spillovers through the effects
of scope on infra-marginal products:∂Π(j, k)
∂k

Z k
=
0

∂ π̃(j, i)
di + π̃(j, k) = 0.
∂k

(15)

We already have that π̃(j, i) is decreasing in i, so for existence and uniqueness we need only that
infra-marginal spillovers are not increasing with scope faster than marginal product profits are
falling. Sufficiently increasing distribution costs, decreasing marginal returns to demand-scopecomplementarity, or quantity cannibalization would suffice.
The conditions for existence and uniqueness of the set of firms in equilibrium are qualitatively
unchanged from the baseline case. Likewise, aggregate industry quantity Q is again the fixed
point solution for the revised conditions (i) − (iii).

Data Appendix
The data set used in this paper combines data from four different databases, made available by
the National Bank of Belgium: (i) Business Registry, (ii) Foreign Direct Investment Survey, (iii)
Trade Database, and (iv) Prodcom Database.
51
Within firm cannibalism as in Eckel and Neary (2010) would be captured in a strictly negative derivative ofthe last term with respect to qji ; conversely, the spillover (the derivative of the last term with respect to qji )would be zero under demand-scope complementarities (holding k fixed).

45

Carry-Along Trade

Business Registry
The Business Registry covers the population of firms required to file their (unconsolidated)accounts with the National Bank of Belgium. The data combine annual accounts figures withdata from the Crossroads bank on firms’ main sector of activity. Overall, most firms that areregistered in Belgium (i.e. exist as a separate legal entity) and have limited liability are required
to file annual accounts. Specifically, all limited-liability firms that are incorporated in Belgium
have to report unconsolidated accounts involving balance sheet items and income statements.
Belgian firms that are part of a group additionally have to submit consolidated accounts where
they report the joint group’s activities in a consolidated way. However, Belgian affiliates thatbelong to a foreign group and that do not exist as a separate legal entity in Belgium are notrequired to report unconsolidated accounts (they are required to file a consolidated account,but these data do not allow us to obtain firm-level characteristics specifically for the Belgian
affiliate). This implies that whenever these firms are exporters, they will be included in theanalysis when using the full export sample, but cannot be included in the sample when we
combine the trade data with firm characteristics or when we introduce a sample selection basedon firms’ main sector of activity (since this information is recorded in the Business Registrydatabase).
There are two types of annual accounts: full and abbreviated. Firms have to file a fullannual account when they exceed at least two of the following three cutoffs: (i) employ at least
50 employees; (ii) have an annual turnover of more than e7.3million; and (iii) report total assets
of more than e3.65million. An important difference between the two types of accounts is that fullaccounts distinguish between total turnover and total material costs, while abbreviated accounts
only report value-added (although firms can report turnover and material costs on a voluntarybasis if they choose to do so). Hence, whenever we calculate firm-level productivity, measured aslabor productivity or total factor productivity, we will use value-added as the preferred measureof output. This implies that labor productivity will be defined as value-added per worker andtotal factor productivity indices are calculated using a value-added decomposition in each year.

Foreign Direct Investment Survey
The Foreign Direct Investment Survey data contain information on firms’ foreign shareholders
and affiliates. Since 2001, only firms with financial fixed assets of more than e5 million or total
equity value of more than e10million or a balance sheet total exceeding e25million are required
to report. We use the FDI survey to identify firms’ foreign shareholders and affiliates.

46

Carry-Along Trade

Trade Database
The Trade Database covers the full population of firms that reported trading activities in 2005.
The data include both import and export flows, at the firm-product-country level. In addition,
the data distinguish between intrastat (intra-EU) and extrastat (extra-EU) trade and between
different types of transactions (e.g. transactions with transfer of ownership and compensation,transactions involving repairs and return of goods, transactions before processing and repair,etc.).
Whether firms have to report their export transactions, depends on the value and destinationof export flows. For intra-EU trade flows, firms have to report their trade on a monthly basis,using an electronic submission system. Firms are only required to report intrastat trade if theirvalue of trade exceeds a particular cutoff. The participation of firms in the intrastat inquiry(pertaining to the intra-EU trade) is determined by statistical thresholds (selection is basedon the VAT returns from the previous year). For 2005, firms exporting or importing for morethan e250,000 a year have to report their export transactions. Estimations performed by the
National Bank of Belgium suggest that total trade reported in the Trade Database accounts formore than 98 percent of total actual exports.
For trade flows destined for countries outside of the European Union (extrastat trade), data
are collected from customs records. Usually these data are collected on a transaction basis,though a few companies are exempted and file a monthly declaration with the NBB. The customs
declarations are collected on a daily basis and aggregated by the NBB. For extrastat trade, alltransactions whose value is higher than e1,000 or whose weight is bigger than 1,000Kg haveto be recorded. Each observation represents an export or import flow (intrastat or extrastat)of a particular 8-digit Combined Nomenclature (CN8) product to or from a particular country
by an individual firm. We exclude all trade transactions that do not involve a “transfer ofownership with compensation” from the data such as re-exports, the return, replacement andrepair of goods, transactions without compensation (e.g. government support), processing or
repair transactions, etc.

Prodcom Database
The Prodcom Database covers the population of firms that declared their production activities
in 2005. The data contain firms’ production activities at the firm-product level. All firms
employing at least 10 people and with primary manufacturing activity are required to report to
Prodcom. Firms with primary acitivity outside the manufacturing sector are only required toreport if they employed at least 20 people. Firms below the employment cutoff are only required
to report if their turnover exceeds a minimum threshold. Whether or not firms have to file a47

Carry-Along Trade

Prodcom declaration is based on their social security records of the previous year. The Prodcom
survey is obligatory and its underlying regulation is EU-based. All EU member states (and some
EFTA countries and future accession countries) are bound by the Prodcom regulation.
In the Prodcom declaration, which has to be filed on a monthly basis, firms are required
to record their production activities at an 8-digit level. Products are Prodcom products, i.e.
they are part of the European Prodcom List. Eurostat has developed the Prodcom List withtwo principal goals in mind: (i) measure production in the EU member states on a comparable
basis and (ii) enable a comparison between production and foreign trade statistics (Eurostat,2006). In view of the second aim, the Prodcom List has a close relationship with the Combined
Nomenclature classification, which is used to record foreign trade statistics. In addition, theProdcom classification is closely linked to the European NACE and CPA classifications, i.e. thefirst six digits of the Prodcom codes are CPA codes and the first four digits are NACE codes.

Merging data
To compare firms’ domestic production and trade activities at the product level, we merge thetrade and domestic production data obtained from the Trade Database and Prodcom Databaserespectively. Both databases use firms’ VAT number to identify firms, but a different classification system is used to record products. The Trade Database defines products using the
Combined Nomenclature (CN8) classification at 8-digit level, while the Prodcom Database defines a product using the Prodcom classification at 8-digit level (PC8). Although there is a close
link between the CN and PC classification by construction, the Prodcom list does not cover all
products listed in the CN classification and vice versa. Specifically, the Prodcom list does notcover certain CN products (e.g. energy and recycling products), while the CN classification does
not cover industrial services (some of which are covered by Prodcom). When we translate bothclassifications into HS6+ products, we only take products covered by both classifications into
account. A detailed discussion of the issues confronted when merging production and trade canbe found in Van Beveren et al. (2012).
Firm-level data from the combined Prodcom-Trade data are additionally merged with theBusiness Registry data and FDI survey data, using the VAT number as the firm identifier. The
final data set contains data on all firms that produced at least one product in the Prodcom
survey (5465 in 2005). Of these 5465 firms, 3631 are exporters.

48

Carry-Along Trade

Table 1: Summary statistics: Cross-section sample for 2005

Total exports
Number of firms

Value of exports

Number of
products
exported
1
2
3
4
5
6
7
8
9
10

N
7,068
2,874
1,760
1,210
941
785
586
496
443
367

% of total
33.9
13.79
8.44
5.8
4.51
3.77
2.81
2.38
2.12
1.76

Value
(€ 1,000,000)
4,169
5,118
4,220
4,880
6,648
6,937
7,096
5,281
7,655
2,711

% of total
2.14
2.63
2.17
2.51
3.42
3.56
3.65
2.71
3.93
1.39

1-5
6-10
11-15
16-20
21-25
25-30

13,853
2,677
1,321
777
488
362

66.45
12.84
6.34
3.73
2.34
1.74

25,03529,68027,387
24,323
6,913
10,225

12.86
15.25
14.07
12.50
3.55
5.25

Average
Average
Average number Exports per Exports at the Average exports
Firm-Product- Firm-Productof export
at the FirmCountry
Leveldestinations per
Country level(€ 1,000)(€1,000)
firm(€ 1,000)
1.82
324
590
324
3.56
397
890
500
5.00
326
799
480
6.55
386
1,008
616
7.38
517
1,413
958
9.19
497
1,473
962
10.40
551
1,730
1,164
10.94
417
1,331
973
10.66
669
1,920
1,620
11.93
251
739
619
3.37
10.40
12.87
15.78
15.90
18.17

390
481
557
532
202
311

906
1,452
1,627
1,749
622
1,016

1-10
16,53079.29
54,715
28.11
4.51
434
1,138
11-20
2,098
10.06
51,710
26.57
13.95
545
1,682
21-30
850
4.08
17,139
8.81
16.87
255
810
31-40
406
1.95
9,835
5.05
18.63
221
690
41-50
274
1.31
8,553
4.39
21.61
185
689
>50
690
3.31
52,692
27.07
25.33
158
668
Total
20,848100.00
194,643100.007.15
273
947
Products are defined as HS6+ products. For information on sample selection and product definitions, see the Data Appendix.

49

536
1,066
1,611
1,983
891
1,555
734
1,767
1,196
1,300
1,444
3,015
1,305

1,713
761
376
224
134
107

1-5
6-10
11-15
16-20
21-25
25-30

1.75
2.55
3.06
3.93
3.87
4.80

1.46
1.58
1.85
2.2
2.17
2.45
2.38
2.35
2.95
2.83

# Produced
Products

10,99916,021
10,218
7,766
3,951
5,453

1,112
1,428
1,719
2,769
3,971
2,922
4,639
1,288
5,615
1,557

Exports(million €)

6.42
21.05
27.18
34.67
29.49
50.96

Averageexports per
firm (million €)
1.94
3.69
5.95
10.61
19.66
13.16
26.51
10.06
42.86
14.83
22,044
22,21815,385
11,080
5,607
8,022

3,498
4,207
4,411
4,592
5,336
4,749
6,070
2,127
6,850
2,421

Production(million €)

12.87
29.20
40.92
49.46
41.84
74.97

6.09
10.87
15.26
17.59
26.42
21.39
34.69
16.62
52.29
23.06
7.45
15.59
19.91
23.49
24.70
27.75

3.96
7.39
8.78
9.93
12.43
14.21
15.83
14.95
15.66
18.77
0.04
0.09
0.11
0.11
0.15
0.18

0.02
0.05
0.04
0.03
0.06
0.10
0.07
0.11
0.08
0.08
14.41
14.94
15.16
15.47
15.42
15.68

14.13
14.44
14.51
14.70
14.65
14.85
14.92
14.82
15.12
15.06
3.38
3.83
4.04
4.29
4.26
4.45

3.15
3.40
3.43
3.63
3.60
3.75
3.73
3.76
4.01
3.98

Average production Average # ln(Total Factor ln(Valueln(Employment)
per firm (million €) destinations Productivity)
added)

1-10
2,474
2.00
27,02010.92
44,262
17.89
9.96
0.05
14.58
3.52
11-20
600
3.39
17,98429.97
26,465
44.11
21.24
0.11
15.28
4.13
21-30
241
4.28
9,404
39.02
13,628
56.55
26.05
0.16
15.53
4.34
31-40
104
4.15
4,449
42.77
5,285
50.81
32.77
0.26
16.13
4.81
41-50
74
5.28
4,533
61.25
4,085
55.21
35.64
0.17
16.20
4.96
>50
138
8.76
21,624156.7023,818172.59
47.98
0.35
17.01
5.59
Total
3,631
2.76
85,014
23.41
117,544
32.37
15.51
Notes: This table includes all exporters in the Prodcom survey for 2005 that report positive domestic production for at least one of their products. Products are defined as HS6+
products.

574
387
289
261
202
222
175
128
131
105

# Firms

1
2
3
4
5
6
7
8
9
10

# Exported
Products

Carry-Along Trade

Table 2: Summary statistics, Prodcom Firms: 2005

50

Carry-Along Trade

Table 3: CAT Firms, Products and Exports: 2005

CAT Firms
Firms with at least 1 Pure CAT product

HS6+
3,233
3,177

HS4+
3,081
3,030

HS2+
2,745
2,669

Total Products
CAT Products

2,858
2,822

1,012
999

90
90

Firm-Products
CAT Firm-Products
Exports of CAT products (million €)Produced Exports (million €)Sourced Exports (million €)45,13439,286
41,47559,62825,38634,08929,11834,39265,373
19,641

17,643
13,66831,97470,900
14,114

Notes: There are 3631 exporting firms. Total exports in the sample amount to €85,014 million. CAT Firms andFirms with at least 1 PURE CAT product are firms that export at least one CAT product and at least one pure
CAT product respectively. Total Products is the number of unique products exported and Firm-Products is thetotal number of unique firm-product pairs exported. CAT Products is the number of products exported as a CAT
product by one or more firms and CAT Firm-Products is the number of unique firm-product pairs exported as a
CAT product. Exports of CAT products are the total exports of all CAT firm-products respectively. Produced
Exports is the produced value of all exported firm-products and Sourced Exports is the non-produced part of allexported firm-products.

51

Carry-Along Trade

Table 4: CN and PC Codes and Descriptions for Sweet Biscuits

CN/HS CodeDescription

1905 31

Sweet biscuits

1905 31 11

Completely or partially coated or covered with chocolate or otherpreparations containing cocoa in immediate packings of a net content
not exceeding 85 g

1905 31 19

Completely or partially coated or covered with chocolate or otherpreparations containing cocoa – other

1905 31 30

Containing 8 % or more by weight of milkfats

1905 31 91

Sandwich biscuits

1905 31 99

Other

PC CodeDescription

10.72.12

Sweet biscuits

10.72.12.53

Sweet biscuits, waffles and wafers completely or partially coated or
covered with chocolate or other preparations containing cocoa

10.72.12.55

Sweet biscuits (including sandwich biscuits, excluding thosecompletely or partially coated or covered with chocolate or otherpreparations containing chocolate)

Notes: The Combined Nomenclature (CN) and Prodcom (PC) classifications are available
at ec.europe.eu/eurostat/ramon5247.65%98.73%

86.39%

29.86%

48.79%

Value of Sourced exports
as % of total exports

Exports of CAT products
as % of total exports% of products exported as
98.74%
CAT by at least 1 firm

% of export firm-products
87.04%
with CAT

53
87.63%

98.67%

50.64%

29.59%

89.91%

2,635

86.49%

98.88%

58.53%

29.09%

87.88%

1,922

85.15%

98.83%

44.27%

31.15%

87.80%

3,114

83.73%

98.99%

50.02%

36.20%

86.26%

1,769

87.76%

98.66%

45.84%

33.53%

90.90%

3,485

82.66%

97.78%

34.98%

24.12%

85.71%

3,534

88.31%

97.80%

37.64%

32.15%

89.19%

3,164

86.85%

98.67%

47.59%

29.86%

88.85%

3,631

Notes: Products are defined as HS6+ products. Manufacturing firms are firms with reported primary activity in NACE (Rev. 1.1) 15 to 37. Firms are part of adomestic group if they are part of a Belgian group. Firms are part of a multinational group if they own foreign subsidiaries or if they are a subsidiary of a foreign
firm (cut-off percentage in ownership: 20 percent). Omitting HS6+ products amounts to omitting all grouped sets of HS6 codes, such that only one-one and manyone mappings between CN/PC and HS6 are retained. Subtracting imports at the firm-product level implies that only exports that are not covered by imports of thesame product by the firm are retained in the data. Alternatively, firm-products with positive imports are dropped from the data altogether. The final column imposes a
cut-off in the definitions for regular and CAT exports to account for potential rounding errors in the data, i.e. exports at the firm-product level are considered as
regular exports if the ratio of domestic production to exports is higher or equal than 0.99. Similarly, firm-products are considered as pure CAT products if the ratio ofdomestic production to exports is lower or equal than 0.01.

27.61%

89.20%

89.04%% of Exporters with atleast 1 CAT product

3,110

3,631

Number of exporting
firms

Manufacturing
Omitting
Only
firms excluding Omitting
Omitting multinational Omitting Subtracting Dropping fp
manufacturing food (NACE domestic multinational and domestic HS6+ imports at with positive Imposing 1%
firms
15)
groupsgroupsgroupscodes
fp-levelimports
cut-off value
Full data

Carry-Along Trade

Table 5: CAT Facts: Robustness

Carry-Along Trade

Table 6: Characteristics of Regular and CAT Exporters: 2005

All Exporters
Employment (fte)Value added (€ million)
Produced Sales (€ million)
All Exports (€ million)
Regular Exports (€ million)ln(TFP)ln(VA/worker)
Multinational
Foreign Ownership# domestically produced products# regular export products# CAT export products# export destinations# of firms

130
12.5
32.4
23.4
12.0
0.09
0.18
0.14
0.13
2.76
1.61
10.82
15.51
3,631

Regular
Exporters
38
2.8
9.9
3.1
3.1
0.05
0.10
0.05
0.05
1.81
1.33
0.00
5.00
398

CAT
exporters
142
13.7
35.1
25.9
13.1
0.10
0.19
0.15
0.14
2.88
1.65
12.15
16.81
3233

Notes: Regular Exporters are firms that export only regular products but no CAT products. CAT
exporters export at least one CAT product. The two categories are mutually exclusive and together equal
the total number of exporting firms. The number of observations differs depending on availability of thefirm-level characteristics. All values reported are sample means, except in the last row, where thenumber of firms is reported.

54

Carry-Along Trade

Table 7: Firm Productivity (TFP), Carry-Along Trade and the Margins of Trade: 2005

Panel A: Total Factor Productivity
All Exportsln(valuef)
Ln(TFP)
Fixed effects
Clustering
Observations
R-squared

1.294***[0.104]
Industry
no
3,097
0.153

ln(# productsf)

ln(average valuef)

0.508***[0.051]
Industry
no
3,097
0.155

0.785***[0.085]
Industry
no
3,097
0.117

Panel B: Total factor productivity
Exports by type (regular or CAT)dCAT
Ln(TFP)
dCAT * Ln(TFP)
Fixed effects
Clustering
Observations
R-squaredln(valuef)

ln(# productsf)

ln(average valuef)-1.109***[0.070]1.215***[0.115]1.269***[0.024]
0.097***[0.033]-2.378***[0.065]1.118***[0.108]-0.101[0.164]
Industry
firm
5,219
0.122

0.409***[0.060]Industry
firm
5,219
0.373

-0.510***[0.145]
Industry
firm
5,219
0.258

Panel C: Labor productivity
Exports by type (regular or CAT)dCAT
Ln(VA/worker)ln(valuef)

ln(# productsf)

ln(average valuef)-1.048***[0.069]1.215***[0.104]1.243***[0.024]0.077***[0.022]-2.290***[0.064]
1.138***[0.101]dCAT * Ln(VA/worker)-0.1720.270***-0.442***[0.124][0.045][0.117]
Fixed effects
Industry
Industry
Industry
Clustering
firm
firm
firm
Observations
5,779
5,779
5,779
R-squared
0.132
0.366
0.263
Notes: Table reports OLS regression of log export value (total - panel A, regular or CAT Panels B and C) and its components on log firm productivity, measured as total factor
productivity (Panels A and B) or labor productivity (Panel C). Panels B and C include adummy for the type of exports (regular or CAT) and an interaction. Regular and CAT
exports are aggregated at the firm level for columns 1-5 in Panels B and C (a firm withboth regular and CAT products features twice). Industry dummies are defined at the twodigit NACE level. Significance levels: *** p < 0.01, ** p < 0.05 and * p < 0.10.

55

Carry-Along Trade

Table 8: Robustness: Firm Productivity, Carry-Along Trade and the Number of Products: 2005

Dependent variable: Number of products by type (regular or CAT)log of total production
value of the firm

Productivity proxies
log of production value
log of total export value log of export value ofof largest producedof the firmlargest export productproduct
1.224***
1.046***
1.066***[0.025][0.023][0.024]dCAT

1.249***[0.025]Ln(measure of productivity)

0.129***[0.010]0.059***[0.010]0.067***[0.006]

0.043***[0.006]dCAT * Ln(productivity)

0.137***[0.018]0.189***[0.018]0.192***[0.010]0.182***[0.010]

Fixed effects
Clustering
Observations
R-squared

Industry
firm
5,219
0.423

Industry
firm
5,219
0.406

Industry
firm
5,219
0.491

Industry
firm
5,219
0.455

Notes: Table reports OLS regression of log number of exported products (regular or CAT) on a dummy for thetype of exports (regular or CAT), a proxy for firm productivity and an interaction. All productivity proxies aredefined relative to the industry mean. Industry dummies are defined at the two-digit NACE level. Significancelevels: *** p < 0.01, ** p < 0.05 and * p < 0.10.

56Carry-Along Trade

Table 9: Export Prices and the Number of Exported Products: 2005

ln(# of products)fc

OLS
0.113***[0.010]# of productsfc-

ln(export quantity)fpc
Tariffpc
Number of observations
R2
F-stat first-stage regression
Country fixed effects
Country-Product fixed effects
Firm-product fixed effects

Dependent variable: Log export price (firm-product-country)
IV
OLS
IV
OLS
IV
OLS
0.523***
0.113*** 0.754***[0.114][0.018][0.192]-0.006***[0.001]

0.068***[0.017]--0.006***[0.002]IV
0.085***[0.026]-0.196*** -0.231*** -0.191*** -0.239*** -0.205*** -0.257*** -0.200*** -0.261***[0.004][0.011][0.004][0.015][0.006][0.021][0.006][0.021]-0.002**[0.001]
31035
0.211
99
4573

-0.001*[0.001]
31035
17.33
99
4573

-0.002***[0.001]
31035
0.207
99
4573

-0.001**[0.000]
31035
10.24
99
4573

-

-

-

-

18784
0.225
6764
3946

18784
30.85
6764
3946

18784
0.222
6764
3946

18784
16.69
6764
3946

Note: The number of products is defined as the total number of export products of a firm to a specific destination (including HS6 and HS6+ categories). The
estimation sample only includes export flows destined for countries outside the EU (extra-EU exports) and HS6 products (more aggregate HS6+ groups areomitted). Cases where only a single observation features in a fixed effect (country or country-product and firm-product) are omitted from the sample (this explains
the lower number of observations when country-product fixed effects are included). Due to the large number of fixed effects, all specifications are estimated indifferences (demeaned). Standard errors (and F-statistic in first stage) have been adjusted to take demeaning into account, they are robust and clustered at the firmproduct level. Instrument in the first stage regression is the (unweighted) average tariff across all products produced or exported to any destination by the firm and isdefined at the firm-country level. Significance levels: *** p < 0.01; ** p < 0.05; * p < 0.1.

57