Why do nations trade? If two countries are each capable of producing
the same set of commodities, why should they go to the trouble and expense
of exchanging them? More concretely, how can economists explain why
France and Germany, for example, ship agricultural goods, machinery
and other products across their mutual border, when each country could
reasonably take care of its own needs? And how do these trade patterns
help explain where industries will locate?
Since the early 19th century, economists have used the theory of comparative
advantage to answer such questions. According to this classic theory,
nations are made better off through trade by capitalizing on their inherent
differences in natural resource or capital endowments. If two nations
differ in land fertility and mineral resources, for example, it makes
economic sense for one of them to specialize in growing vegetables and
trade some of them to the other country for a commoditysteel,
perhapsthat that country can produce more efficiently because
of its inherent advantages. (It's a bit trickier than that, actually;
But over the last 20 years, international trade economics has undergone
what some have termed a "revolution" because of a new theory
that gives very different answers to the same kinds of questions. This
new trade theory is often summed up in the simple words "increasing
returns"shorthand for "increasing returns to scale,"
a term synonymous with "economies of scale."
The new theory, then, is the idea that trade arises to take advantage
of economies of scale: Industries in each country can achieve lower
unit costs by producing in large volume and spreading the high start-up
expenses (for example, research and development, machinery purchases)
over many, many units. If confined to the domestic market, an industry
might not be able to achieve the highest level of scale economies, but
by producing for both domestic and foreign markets, sufficient volumes
can be produced to reap greater economies of scale.
According to this theory, two countries could both get cheaper cars
and lamps, for instance, if one specialized in automobile manufacturing
and the other devoted its resources to making lighting equipment, regardless
of the inherent resource endowments of those countries. By taking advantage
of increasing returns to scale, each country could produce its specialty
at low unit costs and then trade with the otherboth countries
will gain through trade, but not because of comparative advantage.
An incomplete revolution
This "revolution" in trade theory, however, is partial and
unfinished. Economists generally agree that the new increasing-returns
theory has its strengths, but they disagree deeply about how important
it is relative to comparative advantage theory. After all, nations often
trade products whose manufacture isn't subject to increasing returns
to scalethat is, commodities that can be produced at either constant
returns (that is, doubling inputs results in exactly twice the output)
or diminishing returns (doubling inputs results in less than twice the
output). Comparative advantage theory can explain that kind of trade,
but increasing-returns theory can't. So how well do the two theories
explain what goes on in the real world?
Economists also hotly debate one of the most significant corollaries
of increasing-returns theory, the so-called home market effect. This
theory helps explain where industries will set up their operationsan
issue of great consequence to politicians and labor unions as well as
economists. In brief, it says that factories will tend to locate close
to their largest markets so that they can minimize overall shipping
costs while still taking advantage of economies of scale. That is, car
companies will locate in Germany rather than France if it's clear that
Germans are likely to buy more cars. That way the company can produce
low-cost cars and not have to pay much to ship them to its largest market.
Just a few years ago it appeared that the home market effect hypothesis
had been dealt a mortal blow. An insightful critique seemed to have
found an Achilles' heel in an ostensibly innocuous assumption that underlay
the mathematical model of increasing-returns trade theory. If the assumption
were changedas seemed empirically reasonablethe home market
But with a recent paper, "The Home Market and the Pattern of Trade:
Round Three" [Minneapolis Fed Research Department Staff
Report 304], two Federal Reserve economists have revived the home
market component of increasing-returns trade theory by illustrating
that the critique itself rested on an untenable assumption. The paper,
by University of Minnesota economics professor Thomas J. Holmes, a visiting
scholar at the Minneapolis Fed, and John J. Stevens, an economist at
the Fed's Board of Governors, finds that this fundamental outcome of
the increasing-returns trade "revolution" remains entirely
valid. Yet at the same time, the economists suggest that
increasing-returns trade theory and the home market effect may have
their greatest explanatory power not at the global level, but much closer
A quick trade trip
This tale of theoretic death and resurrection requires a bit more background,
thougha brief economic primer on trade models, old and new.
According to the classic theory of comparative advantage, nations, regions,
cities and even individuals will exchange goods based on their relative
levels of labor productivity, which inherently differ because available
technologies and natural endowments vary among trading partners.
If England and Portugal, for example, can both produce wool and wine,
it might seem there would be little reason for either country to pack
up one commodity and ship it off to the other nation. But comparative
advantage theory demonstrates that, in fact, both parties can benefit
economically by trading those goods. And this is true even if one of
themPortugal, say, because of its sunny climateis able to
produce both goods using less labor than the other nation (that is,
even if it has an absolute advantage in production of both goods).
Describing commodity exchange under comparative advantage is invariably
confusing, but in a nutshell, each nation can obtain as much or more
of both goods by taking advantage of the countries' differing ratios
of labor productivity for the two goods. Each country should determine
which productwine or woolit can produce more efficiently
than the other nation (relative to its own efficiency in producing the
other good) and exchange it for the product that its trading partner
produces more efficiently. Put differently, each nation should specialize
in production of the good for which its opportunity costs are lower
than its trading partner's and import that for which its opportunity
costs are higher.
A clearer example: With his height and athletic ability, Michael Jordan
is undoubtedly better at both basketball and window washing than I am.
(He has an absolute advantage in both.) But we'd each benefit if he
paid me to clean his windows, and I gave up my hoop dreams to watch
him specialize in his comparative advantage. He'd be sacrificing much
less of his overall productivity by getting me to wash his windows and
devoting himself to basketball. And frankly, neither of us would really
miss my slam dunk attempts, but I can do a passable job with a squeegee.
Through specialization and trade, both parties would come out ahead:
clean windows and world-class basketball. [See sidebar
for a fuller explanation of comparative advantage.]
Comparative advantage theory has great strength in explaining something
not intuitively obvious, and it has held sway in economics since the
early 1800s when Robert Torrens and David Ricardo developed it. Ricardo
focused on labor productivity relative to trade. Relatively recent elaborations
(for example, the Heckscher-Ohlin theory) emphasize the importance of
national endowments of capital, as well as labor, and hold that countries
will export goods that use their abundant factor intensively and import
those that use their scarce factor intensively.
But comparative advantage has its weaknesses as well. It has little
ability to explain why regions with similar productivity levels trade
to the extent they dowhy Europe and the United States, for example,
trade in such great volume. Nor does it shed light on intra-industry
trade: the fact that Germany and Japan will trade automobiles with one
another. Indeed, much recent discussion suggests that the theory itself
may have its best advantage in explaining trade between industrialized
and developing nations, but not among countries with similar factor
New trade theory
In the 1980s, economists Paul Krugman, now at Princeton University,
and Elhanan Helpman at Harvard University, among others, began to develop
a new theory of trade that redressed the weaknesses of comparative advantage.
This "new trade theory" is based on the idea of increasing
returns to scale.
Nations with similar factor endowmentsthat is, with little in
the way of comparative advantage differencesmay nonetheless find
it beneficial to trade because they can take advantage of massive economies
of scale, a phenomenon prevalent in a number of economically important
industries. In the pharmaceutical and automobile industries, for example,
the first unit is very expensive to produce, but each subsequent unit
costs much less than the one before because the large setup costs can
be spread across all units.
The mathematics behind increasing-returns trade theory are complex,
but the idea itself is quite intuitive. A trading partner can develop
an industry that has increasing returns to scale, produce that good
in great quantity at low average unit costs, and then trade those low-cost
goods to other nations. By doing the same for other increasing-returns
goods, all trading partners can take advantage of large economies of
scale through specialization and exchange.
A key result of the theory is the home market effect: Countries will
specialize in products for which there is large domestic demand. The
reason here is also intuitive: By locating close to its largest market,
an increasing-scale industry can minimize the cost of shipping its products
to its customers. (On the other hand, constant-returns-to-scale industries
have little need to locate close to large markets. Their unit costs
will be similar regardless of quantities produced. So each market can
efficiently produce such goods locally.)
But the home market effect also has a disturbing implication. If increasing-scale
industries tend to locate near their largest markets, what happens
to small market areas? Other things equal, they're likely to become
"deindustrialized" as factories and industries move to take
advantage of scale economies and low transportation costs. Trade,
therefore, could lead to small countries and rural areas becoming
peripheral to the economic core, the backwater suppliers of commodities.
(As Canadian critics have phrased it, "With free trade, Canadians
would become hewers of wood and drawers of water.") But of course,
economists caution, other things aren't strictly equal: Comparative
advantage effects exist alongside the influence of increasing returns,
so the end result of open trade is not a foregone conclusion.
A revolution blunted
Over the last two decades, new trade theory has had an enormous influence
on international trade economics. It has helped explain trade patterns
among industrialized nations and within industries. It also sheds
light on regional patterns of trade: commodity exchange and industry
location within countries. But in 1998, a paper by Harvard
economist Donald Davis dealt this flourishing movement what seemed
a damaging blow.
Krugman had developed his increasing-returns trade theory by looking
at a model with two sectors, one, alpha, with increasing returns
to scale and the other, beta, with constant returns. To render the
mathematics straightforward, he adopted what he considered a harmless
assumption. "For simplicity," Krugman wrote in his seminal
1980 paper, "also assume that beta goods can be transported costlessly."
It was the kind of simplifying assumption that theorists make all
the time, abstracting somewhat from the real world in order to increase
explanatory power"sacrificing some realism to gain tractability,"
Krugman wrote. And he believed this assumption, if slightly less than
realistic, was basically innocuousnothing vital seemed to hinge
But in his 1998 paper, Davis, now chair of Columbia University's economics
department, examined the assumption more carefully. Reviewing data
on trade costs (including costs of transportation, nontariff barriers,
"border effects" and other costs inherent to trade), Davis
concluded that Krugman's simplification was unrealistic: "There
is little suggestion that total trade costs are higher" for increasing-returns
goods, he wrote. If anything, the cost of trading constant-returns
goods is likely to be higher than that for increasing-returns goods.
Even more crucially, Davis found that the simplification was far from
innocuous; something important does hinge on it. In fact, if Krugman's
model is duplicated with just one small change: Assume that both
sectorsnot just the increasing-returns sectorhave positive
transportation costs, then Krugman's striking finding about trade
and industry location evaporates. When "the industries have identical
trade costs, the home market effect disappears," Davis concluded.
"Industrial structure then does not depend on market size."
By undermining the home market effect, Davis' finding struck at the
heart of new trade theory, so he was careful to note that further
empirical and theoretic investigation was called for. "The importance
of the home market hypothesis for production and trade structure is
such that more extensive inquiry is in order," he wrote.
Viva la revolucion!
Holmes and Stevens answer the call for further investigation by subjecting
Davis' critique to the same close scrutiny he gave Krugman's model.
And similarly, they find that "a seemingly innocuous simplifying
aspect of the Davis model is actually crucial." Just as Krugman
had derived his model using an assumption of conveniencethat
the constant-returns sector had no transportation costsDavis
had built a model with a simplifying assumption: that here are just
two types of industries, one with constant returns to scale and the
other with increasing returns.
Holmes and Stevens alter this assumption by creating a more flexible
model, one that allows for a range of industry types that vary in
their degree of increasing returns. Clearly, all industries aren't
either of a constant scale or a single increasing scale; industries
vary tremendously. The Holmes-Stevens model thus provides a broader,
more realistic description of an economy. And when they use this model
to explore the effects of trade, they find that Krugman's initial
finding reasserts itself: "The pattern of trade here does depend
on country size, just like the original Krugman result."
Specifically, Holmes and Stevens assume (as did Davis) that transportation
costs are positive and identical in all industries, and they find
that industries with low levels of scale economies aren't traded,
while those with medium or high degrees of increasing returns are
traded. According to their model, smaller countries will export medium
increasing-returns products and larger countries will export high
As an example, they say, think about wool as a constant-returns industry,
food processing as a medium economies-of-scale industry and automobiles
as high economies of scale. "We find that opening of trade between
New Zealand [a small market] and Japan [a large market] causes New
Zealand to shift into food processing out of autos, to export food
processing and import autos," they wrote. The wool industrybecause
neither nation has an economies-of-scale advantage in itwill
not trade internationally (or at least, not because of increasing
Thus, Holmes and Stevens give new life to a threatened theory. But
the question remains, to what degree is this theory relevant to the
real world? The increasing-returns explanation for trade never aspired
to replace the comparative advantage explanation; it just supplemented
it. But is increasing returns a minor or major factor in determining
patterns of trade? And where does it have its greatest impact?
Think local, not global
In a recent interview, Holmes said that new trade theory may be both
more powerful and more easily tested at the regional level than at the
international level. Because the theory looks at the influence of market
size on trade patterns and industry structure, it should have its strongest
measurable effects across markets of widely varying sizes and densities.
"If you look at the European Union and the United States, you see
they are fairly similar in terms of market size and overall population
density," Holmes said. "But if you compare Minneapolis and
some place in North Dakota, you see population density differences of
many orders of magnitude." So industry locations and trade at the
regional level are where increasing returns "is going to have its
For example, in another recent paper, Holmes looked at data for nearly
30,000 branch sales offices of manufacturers in the United States and
found that the offices were highly concentrated in large cities, not
spread out evenly across the nation. His preliminary analysis indicated
that the home market effectlocating offices in the largest markets
so as to capitalize on returns to scale and minimize transportation
costsaccounts for a third to a half of that concentration.
A number of studies have looked at international patterns of trade to
gauge the relative importance of comparative advantage and increasing
returns in explaining trade among nations. Davis, in a 1996 paper
with David Weinstein, then at the University of Michigan, looked at
trade patterns in Organisation for Economic Cooperation and Development
member countries and found that the data strongly rejected the increasing-returns
explanation in favor of a comparative advantage explanation. But a few
years later, Davis and Weinstein used what they called a "richer"
geographic model on the same data and reversed their position, finding
compelling evidence of the influence of increasing returns on trade.
A 2002 study by Werner Antweiler at the University of British Columbia
and Daniel Trefler at the University of Toronto looked at trade flows
among 71 countries from 1972 to 1992 and reached similar conclusions.
A cautious revival
Notwithstanding this research, Holmes suggests that data limitations
have prevented the kind of detailed analysis necessary to reach a
conclusive understanding of the importance of increasing-returns effects
at the international level. "To look at these issues, you really
need to get data that is disaggregated to a fine level of industry
detail," he said. "But most of the research in this literature
uses international trade data sets where industries are highly aggregated
to broad levels like 'transportation equipment' or 'chemicals.' That
impedes progress in trying to understand how this is working."
Increasing-returns models, after all, emphasize the importance of
factory specialization and product differentiation. If the data don't
measure that differentiation, they can't fully gauge the effect of
increasing returns. Nations taking advantage of economies of scale
may trade, for example, in Toyotas and Fords. Both autos, true, but
they're very distinct products and most trade data don't reflect the
"In terms of applying this to international [trade], I think
the theory is ahead of the empirical work," observed Holmes.
Data limitations and the relatively weak influence of increasing returns
at the international level may stand in the way of rapid progress
in verifying the theoretical models.
"It's really a hard question to address, trying to sort out the
importance of size from comparative advantage," said Holmes.
And ironically, this economist who helped breathe new life into increasing-returns
trade theory remains quite cautious about its significance for understanding
world trade. "At the international level, in terms of applied
work, I think we're still in its infancy," he said. "We
don't yet have a smoking gun that this is what's really important."