I n t h I s c h a p t e r y o u w I l L

diminishing returns:
As the stock of capital rises, the extra output produced from
an additional unit of capital falls. In other words, when workers already have a
large quantity of capital to use in producing goods and services, giving them an
additional unit of capital increases their productivity only slightly. Because of
diminishing returns, an increase in the saving rate leads to higher growth only for
a while. As the higher saving rate allows more capital to be accumulated, the ben-
efits from additional capital become smaller over time, and so growth slows down.
In the long run, the higher saving rate leads to a higher level of productivity and income,
but not to higher growth in these variables.
Reaching this long run, however, can take
quite a while. According to studies of international data on economic growth,
increasing the saving rate can lead to substantially higher growth for a period of
several decades.
The diminishing returns to capital has another important implication: Other
things equal, it is easier for a country to grow fast if it starts out relatively poor.
This effect of initial conditions on subsequent growth is sometimes called the
catch-up effect.
In poor countries, workers lack even the most rudimentary tools
and, as a result, have low productivity. Small amounts of capital investment would
substantially raise these workers’ productivity. By contrast, workers in rich coun-
tries have large amounts of capital with which to work, and this partly explains
their high productivity. Yet with the amount of capital per worker already so high,
additional capital investment has a relatively small effect on productivity. Studies
of international data on economic growth confirm this catch-up effect: Controlling
for other variables, such as the percentage of GDP devoted to investment, poor
countries do tend to grow faster than rich countries.
This catch-up effect can help explain some of the puzzling results in Figure 24-1.
Over this 31-year period, the United States and South Korea devoted a similar
share of GDP to investment. Yet the United States experienced only mediocre
growth of about 2 percent, while Korea experienced spectacular growth of more
than 6 percent. The explanation is the catch-up effect. In 1960, Korea had GDP per
person less than one-tenth the U.S. level, in part because previous investment had
been so low. With a small initial capital stock, the benefits to capital accumulation
were much greater in Korea, and this gave Korea a higher subsequent growth rate.
d i m i n i s h i n g r e t u r n s
the property whereby the benefit
from an extra unit of an input
declines as the quantity of the
input increases
c a t c h - u p e f f e c t
the property whereby countries
that start off poor tend to grow
more rapidly than countries
that start off rich

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5 4 0
PA R T N I N E
T H E R E A L E C O N O M Y I N T H E L O N G R U N
This catch-up effect shows up in other aspects of life. When a school gives an
end-of-year award to the “Most Improved” student, that student is usually one
who began the year with relatively poor performance. Students who began the
year not studying find improvement easier than students who always worked
hard. Note that it is good to be “Most Improved,” given the starting point, but it is
even better to be “Best Student.” Similarly, economic growth over the last several
decades has been much more rapid in South Korea than in the United States, but
GDP per person is still higher in the United States.
I N V E S T M E N T F R O M A B R O A D
So far we have discussed how policies aimed at increasing a country’s saving rate
can increase investment and, thereby, long-term economic growth. Yet saving by
domestic residents is not the only way for a country to invest in new capital. The
other way is investment by foreigners.
Investment from abroad takes several forms. Ford Motor Company might
build a car factory in Mexico. A capital investment that is owned and operated by
a foreign entity is called