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VOL. 13, NO. 2 • FEBRUARY 2018

DALLASFED

Economic
Letter
Global Interfirm Network Reveals
Centrality of U.S. and Financial Sector
by Everett Grant and Julieta Yung

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ABSTRACT: The global interfirm
network indicates the level of
integration among firms across
industries and regions, which
intensified with globalization in
recent decades. While there
is evidence of direct contagion
passing between firms in
the network, there are also
indications that connectedness
plays a role in a reduced
likelihood of firm distress and
improved performance.

I

ntegration across firms—
including greater international
connectivity—has increased
over the past three decades.
While the unprecedented
worldwide global financial crisis highlighted the extent of connectedness, its
implications beyond crises and recessions have fostered a renewed interest
in understanding the transmission of
shocks across countries and industries.
The global interfirm network reveals
that firms are most connected with those
in the same industry and country, and
the U.S. and the financial sector are at
the network’s core. Further, the level of
international connectedness has been
especially high over the past decade.
These features are important considerations for policymakers and investors when evaluating possible global
economic spillovers and the potentially
reduced scope for international risk
sharing and portfolio diversification.

Interfirm Connectedness
The exact level of integration
between two firms is difficult to quantify
because there are often simultaneous
linkages across many different dimensions. Not only are interfirm connections difficult to aggregate into a single
connectedness measure, but the task of
collecting such granular data on even a

handful of firms is insurmountable, let
alone doing it in real time.
In an attempt to overcome this challenge, an interfirm network is constructed based on daily equity returns data.
The procedure exploits equity market
efficiency and the idea that large, actively
traded and broadly followed firms’ equity
prices reflect all available information
about them, including proximity via various channels.
For example, consider a firm that
outsources work to another. A negative
shock to the client firm is passed on to
the service provider and is ultimately
reflected by declining equity prices for
both entities.
These connections can be local or
span the globe. Following the March 11,
2011, earthquake and tsunami in Japan,
the local Hitachi engine factory that
manufactured 60 percent of global car
engine airflow sensors shut down. With
most major automobile manufacturers utilizing just-in-time global supply
chains, this single closure amplified the
disruption caused by the natural disaster.
Not only did many Japanese automotive factories close, but several German,
Spanish and American plants did as
well.1
The challenges of estimating the
global interfirm network stem from complications due to the large number of

Economic Letter
firms that need to be included to have a
representative depiction. In this exercise,
equity returns data for hundreds of firms
around the world are collected. State-ofthe-art machine learning techniques—in
particular, methods applicable with very
large data sets—are used to systematically select significant bilateral firm
connections and estimate the degree of
integration among firms.2
In these networks, connections are
based on estimates of the degree to
which the daily equity return of one firm
predicts the next day’s equity return for
another firm. The connections run in
each direction between two firms and
need not be symmetric. This methodology only relies on the equity returns, so it
can be performed in real time and avoids
the need to make assumptions on how
each particular firm relates to the hundreds of other firms in the network.

Centrality of U.S. Firms
Spring plots, a graphic technique borrowed from physics for picturing large
systems of interacting agents, help visualize the network. In these plots, each
firm is represented by a node, or dot. Its
proximity to other nodes indicates how
connected firms are with one another.
Highly connected firms are pulled
toward each other by the larger connec-

Chart

1

tion weights between them, as well as
potentially being attracted by their connections with shared neighboring firms.
For example, two petroleum refiners might not be closely connected with
one another in the network by their
direct linkages; however, if they are both
strongly connected with a single oil
extraction firm, they would end up near
each other on the map.
Chart 1 depicts the distribution of 382
large firms that were continuously traded
from 1991 through 2016 and in the top
1 percent of all global firms by market
capitalization for at least one year—an
interfirm global network. A node’s color
indicates the currency of issuance for
its primary equity, a proxy for the firm’s
geographic region.
Regional groupings are clearly organized in concentric circles, with a central
cluster consisting of the U.S., followed by
the eurozone, the U.K., other advanced
European countries and Canada. The
proximity of firms across these regions
suggests that geographic borders are not
a strong delimiting factor when it comes
to interfirm connectedness.3 Shocks that
affect any of these highly integrated firms
are likely to be reflected in equity return
responses of all of the nearby firms in the
figure, regardless of where a company’s
headquarters is located.

Companies Arrayed in Regional Concentric Circles

On the network periphery are
Australian and Asian firms. These companies tend to be less sensitive to the
types of shocks that would generate large
movements in the equity returns of those
in the core.

Centrality of Financial Firms
Firms not only differ in their currency
of equity issuance but also in the types
of goods and services they produce.
Therefore, each node of the network is
classified by industry instead of region to
examine the relationships among them
(Chart 2). Each firm is in the same location as in Chart 1. The industry-based
node colors reveal a very different pattern of how firms cluster in the network.
Firms within the same industry
tend to group together in a roughly
pie-slice-shaped pattern. Financial and
industrial diversified firms are at the
center of the map, revealing that they
are the most integrated firms, not only
with one another but also with firms in
other industries. Firms in the information, communication and technology
sector are at the top right, followed by
consumer noncyclical, utility, energy and
base materials, and then consumer cyclical firms at the top.
Since the network shows clear (but
different) grouping patterns by industry and locality, it is apparent that both
dimensions play important roles in
establishing the structure of the system.
There appear to be both significant
region- and industry-level shock propagation channels in the interfirm network.

Top Region-Industry Sectors

NOTES: Each colored dot represents a firm in a specific region. Plot covers 1991–2016. Firms in the same region tend to
cluster together in concentric circles.
SOURCE: “The Double-Edged Sword of Global Integration: Robustness, Fragility & Contagion in the International Firm
Network,” by Everett Grant and Julieta Yung, Federal Reserve Bank of Dallas Globalization and Monetary Policy Institute
Working Paper no. 313, May 2017.

2

From the network plots, a handful of region-industry pairs appears to
have outsized network impact. Table 1
sorts region-industry pairings by total
connection weights across all firms. For
example, the No. 1 pair, U.S.–finance, has
a connectedness measure that is more
than double the pair five slots down the
list (U.S.–energy), which in turn has a
connectedness measure that is more
than double the pair five slots below
it (euro area-consumer noncyclical).
This ranking of integration by region
and industry provides insight into how
shocks affecting specific sectors in the
economy may spread.

Economic Letter • Federal Reserve Bank of Dallas • February 2018

Economic Letter
Global Network Evolution

Chart

The evolution of the network of
382 firms in Chart 2 can be separately
estimated over subperiods (Chart 3). A
distinct pattern of consolidation emerges
over time, indicating that the high integration of firms is a relatively recent
phenomenon.
There is evidence of a particularly
large increase in agglomeration from
1997 to 2001 and 2002 to 2006, notably
with European firms moving into the
center, likely reflecting the adoption of
the euro and its associated economic
and political integration.
The 2007–11 subprime mortgage
and eurozone debt crisis period brought
together North American and European
firms, but many Asian firms were far
out on the network periphery and not
as affected. Additionally, it is worth
highlighting that over this crisis period,
energy and base materials were at the
center of the network rather than finance.
Thus, finance’s positioning at the center
of the long-term 1991–2016 network is
not merely a result of the global financial
crisis.

2

Classifying by Industry Creates Pie-Shaped Pattern

NOTES: Each colored dot represents a firm in a specific industry. Firms in the same industry tend to cluster together in a
pie-slice pattern. Plot covers 1991–2016.
SOURCE: “The Double-Edged Sword of Global Integration: Robustness, Fragility & Contagion in the International Firm
Network,” by Everett Grant and Julieta Yung, 2017 Federal Reserve Bank of Dallas Globalization and Monetary Policy
Institute Working Paper no. 313, May 2017.

Table

1

Rank

Top Region–Industry Pairs in the Global Network
Dominated by U.S. and Finance
Region–Industry

Influence
Measure

Rank

Region–Industry

Influence
Measure

1

U.S.–finance

760.3

11

Euro area–consumer noncyclical

143.1

Measuring Systemic Risk

2

U.S.–consumer noncyclical

728.1

12

U.K.–finance

118.7

As the research on global networks
develops, understanding how firms are
connected across industries and countries
is the first step toward measuring systemic
risk and developing strategies to prevent
widespread transmission of shocks.
There is evidence of direct contagion
passing between neighboring firms in the
network but also evidence that increased
network connectedness corresponds
with a reduced probability of firm distress and improved stock returns, lower
credit spreads on corporate debt, higher
profits and greater revenue growth.4
The informational content of movements in equity returns is a valuable
proxy for investors’ wealth of knowledge
about individual firms, which can be
exploited as new machine learning and
econometric techniques facilitate more
rigorous statistical analysis on a large
scale. Recent events have emphasized
the significance of international developments and contagion, prompting policymakers, regulators and investors to take
into account interfirm connections and
the implications of global integration.

3

U.S.–inform., comm., tech.

622.8

13

Euro area–consumer cyclical

92.0

4

U.S.–industrial diversified

515.0

14

Euro area–industrial diversified

82.6

5

U.S.–consumer cyclical

445.4

15

Euro area–inform., comm., tech.

81.6

6

U.S.–energy

367.0

16

Canada–energy

80.7

7

Euro area–finance.

221.5

17

Switzerland–finance

78.8

8

U.S.–base materials

212.5

18

U.K.–consumer noncyclical

59.9

9

U.S.–utilities

190.0

19

Euro area–utilities

57.4

10

Canada–finance

147.8

20

Japan–consumer noncyclical

54.6

NOTES: The influence measure ranks region and industry pairs by the total sum of their connection weights relative to other
firms. U.S. industries are highly connected, as represented by eight of the top 10 pairs. Finance is generally the most integrated
industry across countries.
SOURCE: “The Double-Edged Sword of Global Integration: Robustness, Fragility & Contagion in the International Firm Network,”
by Everett Grant and Julieta Yung, Federal Reserve Bank of Dallas Globalization and Monetary Policy Institute Working Paper no.
313, May 2017.

Grant is a research economist in the Research Department at the Federal Reserve
Bank of Dallas. Yung is an assistant professor of economics at Bates College.

Notes
See, for example, “Stress Test for the Global Supply
Chain,” by Steve Lohr, The New York Times, March 11,
2011, www.nytimes.com/2011/03/20/business/20supply.

1

html?pagewanted=all&mcubz=0 and “Toyota, Struggling
with Part Shortages, to Restart Car Lines,” by Nick Bunkley
and David Jolly, New York Times, March 24, 2011,
www.nytimes.com/2011/03/25/business/global/25auto.
html.
2
For details on the estimation procedure refer to “The
Double-Edged Sword of Global Integration: Robustness,
Fragility & Contagion in the International Firm Network,”
by Everett Grant and Julieta Yung, Federal Reserve Bank of

Economic Letter • Federal Reserve Bank of Dallas • February 2018

3

Economic Letter

Chart

3

Global Network’s Concentration Increases
1992–1996

1997–2001

2007–11

2012–16

2002–06

NOTES: Each colored dot represents a firm in a specific industry during a five-year period. Firms have increasingly clustered toward the center over time.
SOURCE: “The Double-Edged Sword of Global Integration: Robustness, Fragility & Contagion in the International Firm Network,” by Everett Grant and Julieta Yung, Federal
Reserve Bank of Dallas Globalization and Monetary Policy Institute Working Paper no. 313, May 2017.

Dallas Globalization and Monetary Policy Institute Working
Paper no. 313, May 2017. This paper includes a summary
of the literature on network estimation and a more in-depth
investigation of the global interfirm network.
3
The finding that locality is a key factor in structuring
interfirm networks is in agreement with the paper “Estimating Global Bank Network Connectedness,” by Mert Demirer,

DALLASFED

Francis X. Diebold, Laura Liu and Kamil Yilmaz, 2015 Manuscript, Massachusetts Institute of Technology, University of
Pennsylvania, and Koc University. This work finds that when
looking at the top 150 global banks, location—not bank
assets—matters for network structure and proximity.
4
See note 2.

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