The marginal efficiency of capital.
Fuller, Edward W.
INTRODUCTION
Economic calculation plays a central role in Austrian economics and
Keynesian economics. However, the Austrians and the Keynesians each
advocate a different approach to economic calculation. The Austrian
school advances the present value approach to economic calculation in
which the net present value is used to rank investment projects. In
distinct contrast, the Keynesians adopt the rate of return approach to
economic calculation in which the marginal efficiency of capital is used
to rank investment projects. The purpose of this paper is to explain the
marginal efficiency of capital and its implications for macroeconomics.
(1)
NET PRESENT VALUE
Ludwig von Mises and Irving Fisher advocate the present value
approach to economic calculation. According to the present value
approach, the price of an investment project tends to equal the present
value of the project's expected cash flows. Murray Rothbard (p.
489) shows that the present value of an investment project is completely
dependent on the size of the expected cash flows, the timing of the
expected cash flows, and the interest rate. (2) To demonstrate, Alvin
Hansen offers the following numerical example: "Consider the case
of a [wooden bridge] costing $2,000 whose life is only three years and
which offers the prospect of a series of yields of $1,000 in each of
three years" (Hansen, p. 118). The wooden bridge will generate cash
flows of 1,000 per year for three years. If the interest rate is 10%,
then the present value (PV) of the wooden bridge is 2,486.85.
PV = 1000/(1 + .1) + 1000/[(1 + .1).sup.2] + 1000/[(1 + .1).sup.3]
= 2,486.85
Rothbard calls the net present value (NPV) the entrepreneurial
profit. The net present value equals the present value minus the price
of the investment. In Hansen's example the net present value of the
wooden bridge is the present value of 2,486.85 minus the price of 2,000.
NPV = 1000/(1 + .1) + 1000/[(1 + .1).sup.2] + 1000/[(1 + .1).sup.3]
- 2,000 = 486.85
The table below summarizes Hansen's economic calculation.
Competition between investors creates a tendency for the price of
an investment project to equal the present value of the expected cash
flows. Investors will bid up the price of an investment project when the
price is below the present value, and investors will bid down the price
of an investment project when the price is above the present value.
Since the price of an investment project tends to equal the present
value, there is a tendency for the net present value to equal zero. In
Hansen's case, the present value of the wooden bridge is 2,486.85
while the price of the wooden bridge is only 2,000. The net present
value is 486.85. Other investors will be drawn to this entrepreneurial
profit. Competing investors will enter the market and bid up the price
of the wooden bridge to 2,486.85 where the net present value is zero.
Competition between investors creates a tendency for the net present
value of an investment project to equal zero.
There is an important negative relationship between the interest
rate and the present value of an investment project. All else equal, the
present value of an investment project increases as the interest rate
falls. In Hansen's example suppose the interest rate is 5% instead
of 10%. In this case the expected cash flows are discounted at 5%. Since
the expected cash flows are discounted at a lower rate, the present
value increases from 2,486.85 to 2,723.25.
All else equal, the net present value of an investment project
increases as the interest rate falls. In Hansen's example the net
present value increases from 486.85 to 723.25 when the interest rate
falls from 10% to 5%. The NPV schedule lists a project's net
present value at various interest rates. Table 3 is the NPV schedule of
the wooden bridge, and it shows that the net present value of the wooden
bridge increases as the interest rate falls.
The NPV schedule can be represented graphically. A continuous graph
of the NPV schedule is called the NPV profile. In Figure 1, the vertical
axis shows the interest rate and the horizontal axis shows the net
present value. The NPV profile shows the net present value of an
investment project at different interest rates.
[FIGURE 1 OMITTED]
The NPV profile has three properties. First, the NPV profile slopes
downward from left to right. This indicates that the net present value
increases as the interest rate falls. Second, the NPV profile is curved
so that the NPV profile becomes flatter as the interest rate falls.
Third, the NPV profile intersects the interest rate axis at the point
where the NPV is zero.
The net present value is used to compare and rank competing
investment projects in the present value approach to economic
calculation. It is necessary to introduce another investment option to
show how the interest rate affects net present value rankings. Suppose
Hansen can build a more durable bridge by using steel instead of wood.
The steel bridge generates the same size cash flows as the wooden
bridge, but the steel bridge has a longer period of production and a
longer life than the wooden bridge. The price of the steel bridge is
5,000. Starting in time three, the steel bridge will generate a 1,000
cash flow every year until time ten. Table 4 is the steel bridge's
cash flow table and it shows that, compared to the wooden bridge, the
steel bridge is a long-term investment project.
Like the wooden bridge, the net present value of the steel bridge
depends on the interest rate. Table 5 lists the net present value of
both the wooden bridge and steel bridge at various interest rates.
Wealth maximizing investors use the net present value to rank
investment projects. According to the NPV rule, wealth maximizing
investors give the highest ranking to the investment option with the
highest net present value. Table 5 shows that net present value rankings
depend on the interest rate. The wooden bridge has a higher NPV ranking
when the interest rate is greater than 5.48%, but the steel bridge has a
higher NPV ranking when the interest rate is less than 5.48%. In this
example, 5.48% is called the crossover rate because the net present
value of the steel bridge equals the net present value of the wooden
bridge when the interest rate is 5.48%. The crossover rate is the
interest rate at which the projects' net present values are equal.
Fisher calls the crossover rate the rate of return over cost: "This
hypothetical rate of interest which if used in calculating the present
worth of the two options compared would equalize them or their
differences (cost and return) may be called the rate of return over
cost" (Fisher, p. 155).
NPV profiles can also be used to illustrate how NPV rankings depend
on the interest rate. The easiest way to depict how the interest rate
affects NPV rankings is by putting both NPV profiles on the same
diagram. (3)
[FIGURE 2 OMITTED]
The crossover rate is the interest rate at which the two NPV
profiles cross. The wooden bridge has a higher NPV ranking when the
interest rate is above the crossover rate, and the steel bridge has a
higher NPV ranking when the interest rate is below the crossover rate.
The two profiles cross because the steel bridge has a flatter profile
than the wooden bridge. The steel bridge's flatter NPV profile
reflects that the net present value of the steel bridge is more interest
rate sensitive than the net present value of the wooden bridge. When the
interest rate changes by a given amount, the percentage change in the
net present value of the steel bridge is greater than the percentage
change in the net present value of the wooden bridge. In general,
long-term projects are more interest rate sensitive than short-term
projects.
The interest rate regulates the intertemporal allocation of
resources in the present value approach to economic calculation. To
demonstrate, Figure 3 combines the NPV diagram and the loanable funds
diagram. In Figure 3, the interest rate determined in the loanable funds
market is greater than the crossover rate, so the wooden bridge has a
higher NPV ranking. In this case the investor will allocate resources to
the wooden bridge.
[FIGURE 3 OMITTED]
Now suppose there is a change in consumer preferences so that
consumers save more and consume less. The increase in the supply of
savings causes the supply of loanable funds curve to shift to the right,
from S to S'. The increase in saving reduces the interest rate and
increases the amount of investment.
[FIGURE 4 OMITTED]
Figure 4 shows that the increase in saving by consumers changes the
investor's NPV rankings. At the lower interest rate the NPV
rankings tell the investor to allocate resources to the steel bridge.
The lower interest rate changes the NPV rankings because "The price
of a factor which can be used in most early stages and whose marginal
productivity there falls very slowly will rise more in consequence of a
fall in the rate of interest than the price of a factor which can only
be used in relatively lower stages of production or whose marginal
productivity in the earlier stages falls very rapidly" (Hayek, p.
263). Figure 4 shows how the interest rate coordinates the actions of
consumers, savers, and investors by adjusting investors' NPV
rankings to reflect changes in the saving behavior of consumers.
In the present value approach the interest rate determines the
intertemporal allocation of resources. The interest rate is the price
signal that "tells businessmen how much savings are available and
what length of projects will be profitable" (Rothbard, p. 997). The
interest rate tells the investor, through his NPV rankings, whether
consumers prefer short-term or long-term investment projects. Figure 3
illustrates that resources are allocated to the short-term project when
the interest rate is high; Figure 4 illustrates that resources are
allocated to the long-term project when the interest rate is low. Figure
4 shows how a lower interest rate resulting from an increase in saving
changes NPV rankings so that investors allocate resources into longer,
more interest rate sensitive investment projects.
MARGINAL EFFICIENCY OF CAPITAL
John Maynard Keynes advocates the rate of return approach to
economic calculation. In the rate of return approach investors use the
marginal efficiency of capital (MEC) to rank investment projects. Keynes
defines the marginal efficiency of capital as the "rate of discount
which would make the present value ... equal to its supply price"
(Keynes, p. 135). (4) In Hansen's example, the marginal efficiency
of capital is the discount rate which makes the present value of the
wooden bridge equal 2,000. In other words, the marginal efficiency of
capital is the discount rate which makes the NPV equal zero.
The marginal efficiency of capital of the wooden bridge is 23.38%.
When the expected cash flows from the wooden bridge are discounted at
23.38%, the present value equals the 2,000 supply price of the bridge.
Put differently, the net present value is zero when the project's
expected cash flows are discounted at 23.38%. This can be seen using the
NPV schedule. Table 7 shows that the net present value declines as the
interest rate rises, and finally equals zero when the interest rate is
23.38%:
The marginal efficiency of capital can also be found on the NPV
profile. Since the marginal efficiency of capital is the discount rate
that makes the net present value equal zero, the marginal efficiency of
capital is the point at which the NPV profile intersects the y-axis. (5)
[FIGURE 5 OMITTED]
In the Keynesian rate of return framework investment decisions are
made by comparing the marginal efficiency of capital to the interest
rate. The MEC rule is to accept an investment project if the marginal
efficiency of capital is greater than the interest rate. Put
differently, the MEC rule is to accept an investment project if the rate
of return is greater than the cost of capital. In Hansen's example
an investor will only build the wooden bridge if the interest rate is
less than 23.38%. Conversely, The MEC rule is to reject an investment
project if the marginal efficiency of capital is less than the interest
rate. In Hansen's case, an investor will reject the wooden bridge
project if the interest rate (the cost of capital) is greater than
23.38% (the rate of return).
Expectations play an important role in Keynes's theory and the
marginal efficiency of capital is Keynes's outlet for expectations.
According to Keynes, a collapse of the marginal efficiency of capital is
the cause of the economic crisis: "It is important to understand
the dependence of the marginal efficiency of a given stock of capital on
changes in expectation, because it is chiefly this dependence which
renders the marginal efficiency of capital subject to the somewhat
violent fluctuations which are the explanation of the Trade Cycle"
(Keynes, p. 143). The marginal efficiency of capital is completely
determined by the investor's expectations about the size and timing
of future cash flows, so the marginal efficiency of capital collapses
when there is a collapse in cash flow expectations. To demonstrate,
suppose Hansen reduces the cash flow forecast because his expectations
suddenly become more pessimistic. The size of the expected cash flows
drops from 1,000 to 750.
The marginal efficiency of capital collapses from 23.38% to 6.13%
when the cash flow forecast is revised downward. The present value and
the net present value do not change after the collapse in cash flow
expectations. The present value is still 2,000 and the net present value
is still zero after the drop in cash flow expectations. This example
illustrates that Keynes views "the offering price of the capital
good as a given, an unchanging, constant amount, even when
entrepreneurs' profit outlook varies" (Huerta de Soto, p.
555).
The most important problem with the marginal efficiency of capital
is that it contradicts the wealth maximizing net present value
criterion. Keynes (p. 137) and Hansen (p. 118) both erroneously claim
that the rate of return approach is identical to the present value
approach. The NPV diagram shows that the rate of return approach and the
present value approach are related, but they are not identical.
According to John Hicks, "Keynes had three elements in his theory:
the marginal efficiency of capital, the consumption function, and
liquidity preference" (Hicks, p. 142). All of these elements are
captured by combining the Keynesian IS-LM diagram with the NPV diagram.
[FIGURE 6 OMITTED]
In Figure 6 the MEC criterion and NPV criterion yield identical
results. The MEC rule is to assign the highest ranking to the project
with the highest marginal efficiency of capital. Table 5 shows that the
wooden bridge (23.38%) has a higher marginal efficiency of capital than
the steel bridge (7.74%). In Figure 6 the wooden bridge's NPV
profile intersects the y-axis at a higher point than the steel
bridge's NPV profile, so the wooden bridge has a higher MEC ranking
than the steel bridge. Since the interest rate determined in the IS-LM
panel is greater than the crossover rate, the NPV criterion also ranks
the wooden bridge above the steel bridge. Figure 6 and Table 5
illustrate that the net present value and marginal efficiency of capital
give identical rankings when the interest rate is greater than the
crossover rate.
Now suppose there is a change in consumer preferences so that
consumers increase saving by reducing consumption. In the Keynesian
IS-LM model, an increase in saving causes the IS curve to shift to the
left, from IS to IS'. An increase in saving lowers both the
interest rate and income.
[FIGURE 7 OMITTED]
In Figure 7 the MEC criterion and NPV criterion yield contradictory
results. Since MEC rankings do not depend on the interest rate, a lower
interest rate does not change MEC rankings. At the lower interest rate
the wooden bridge has a higher ranking according to the MEC criterion,
but the steel bridge has a higher ranking according to the NPV
criterion. The MEC rankings tell the investor to allocate resources to
the smaller, less interest rate sensitive project; the NPV rankings tell
the investor to allocate resources to the larger, more interest rate
sensitive project. (6) Figure 7 and Table 5 illustrate that MEC rankings
contradict NPV rankings whenever the interest rate is below the
crossover rate.
The present value approach is the wealth maximizing approach to
economic calculation. Since MEC rankings contradict NPV rankings, Keynes
does not provide a wealth maximizing investment demand function:
"Keynes's internal rate of return did not give an investment
demand function according to the maximum present wealth criterion of
choice by investors" (Alchian, p. 941). Figure 7 shows that an
investor using the MEC criterion will not allocate resources to the
project that maximizes wealth. The lower interest rate does not lead the
investor to allocate resources to the long-term project. In the rate of
return approach, the interest rate does not tell investors whether
consumers prefer short-term or long-term projects. In Keynes's
theory of investment the interest rate does not regulate the
intertemporal allocation of resources. Instead the interest rate is just
a hurdle, or obstacle, that prevents investors from increasing
investment. In the rate of return approach, a lower interest rate makes
some projects which were previously unprofitable become profitable, so
the volume of investment rises. By reducing the interest rate to a mere
hurdle, the rate of return approach focuses attention on the volume of
investment and conceals how the interest rate regulates the time
dimension of investment.
The conception of the interest rate as a hurdle rate naturally
leads to a monetary policy of manipulating the interest rate. Keynes
advocates a monetary policy of an artificially low interest rate:
"it is to our best advantage to reduce the rate of interest to that
point relatively to the schedule of the marginal efficiency of capital
at which there is full employment" (Keynes, p. 375). (7) Following
Roger Garrison (p. 165) it is possible to expand Figure 6 to include the
Hayekian triangle. In Figure 8 an increase in the money supply causes
the LM curve to shift to the right, from LM to LM'. An increase in
the money supply lowers the interest rate and raises the level of
income.
[FIGURE 8 OMITTED]
The structure of production is fixed in the Keynesian system, so
the increase in the money supply means "the Hayekian triangle
changes in size but not in shape" (Garrison, p. 162). The fixed
shape of the Hayekian triangle indicates that the interest-rate effect
is absent in Keynes's theory. Consequently, an artificially low
interest rate does not initiate an allocation of resources into
long-term projects. The NPV diagram also depicts that the interest-rate
effect is absent in the Keynesian theory. The increase in the money
supply pushes the interest rate below the crossover rate, but MEC
rankings still favor the short-term project. Since MEC rankings do not
depend on the interest rate, an artificially low interest rate does not
cause the investor to allocate resources into the longer, more interest
rate sensitive investment project. The NPV diagram and the fixed
Hayekian triangle are mutually reinforcing ways of showing that the
interest rate does not regulate the intertemporal allocation of
resources in Keynes's theory.
The NPV diagram reinforces the Austrian critique of Keynes's
monetary policy of manipulating the interest rate. In the Austrian
theory an artificially low interest rate results in the intertemporal
misallocation of resources. In the capital-based framework (Garrison, p.
69) the supply of loanable funds curve shifts to the right, from S to
Sm, when the central bank expands the supply of loans.
[FIGURE 9 OMITTED]
The loanable funds diagram shows that the central bank creates a
double disequilibrium in the loanable funds market when it expands the
supply loans. (8) At the artificially low interest rate the quantity of
loans demanded for investment is greater than the quantity of real
savings supplied. In short, investment is greater than savings. The fall
in saving means consumption rises, so the wedge between saving and
investment depicted in the loanable funds market causes the economy to
produce at a level outside the production-possibilities frontier (PPF).
The simultaneous increase in investment and consumption shown on the PPF
also plays out on the Hayekian triangle:
The tug-of-war between investors and consumers that sends the
economy beyond the PPF pulls the Hayekian triangle in two directions....
investors find the longer-term investment projects to be relatively more
attractive. A less steeply sloped hypotenuse illustrates the general
pattern of reallocation in the early stages of the structure of
production.... At the same time, income earners, for whom the lower
interest rate discourages saving, spend more on consumption. A more
steeply sloped hypotenuse illustrates the general pattern of
reallocation in the final and late stages of production.... In effect,
the Hayekian triangle is being pulled at both ends (by cheap credit and
strong consumer demand) at the expense of the middle--a tell-tale sign
of the boom's unsustainability. (Garrison, p. 72)
The NPV diagram shows that central bank loan expansion causes
entrepreneurial error by falsifying net present value calculations. In
the NPV diagram, central bank loan expansion pushes the interest rate
below the crossover rate and reverses the NPV rankings: "the drop
in the interest rate falsifies the businessman's calculation....
They make some projects appear profitable and realizable which a correct
calculation, based on the interest rate not manipulated by credit
expansion, would have shown as unrealizable" (Mises, p. 550). The
NPV rankings are false because they do not accurately reflect consumer
preferences. The falsified NPV rankings tell the investor that consumers
prefer the long-term project, but consumers actually prefer the
short-term project. The investor commits an entrepreneurial error by
allocating resources to the project that will not satisfy the most
urgent needs of the consumers. This intertemporal misallocation of
resources into long-term projects is called malinvestment. The
artificially low interest rate does not just affect the representative
investor-entrepreneur in the NPV diagram. Since the interest rate is the
universal NPV input, the artificially low interest rate causes a
universal falsification of NPV rankings in favor of longer, more
interest rate sensitive projects. In the Austrian theory, the universal
falsification of NPV rankings causes a massive cluster of investor
error. The NPV diagram and the Hayekian triangle are mutually
reinforcing ways of showing that an artificially low interest rate
results in an unsustainable economic boom.
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(1) The distinction between the present value approach and the rate
of return approach comes from Lorie and Savage (p. 237) and Solomon (p.
124). Both approaches are used widely in practice. Graham and Harvey (p.
33) found that 75% of the financial managers in their study use the net
present value to rank investment projects. They also found that 76% of
the managers in their study use the marginal efficiency of capital.
(2) Rothbard uses different terminology to describe the present
value approach to economic calculation. The term cash flow is identical
to the marginal value product (MVP). The term discounted cash flow is
identical to the discounted marginal value product (DMVP): "The
capitalized value of the capital good is the sum of the future DMVPs, or
the discounted sum of the future MVPs. This is the present value of the
good, and this is what the good will sell for on the capital
market" (Rothbard, p. 491).
(3) See Alchian (p. 939) and Lorie and Savage (p. 237) for more on
the NPV diagram.
(4) Keynes (p. 135) calls an investment's expected cash flows
the prospective yield. Today the marginal efficiency of capital is
better known as the internal rate of return.
(5) The marginal efficiency of capital cannot be used in many
situations. Lorie and Savage (p. 237) and Solomon (p. 127) show that
projects with nonnormal cash flows will have multiple MECs. There are
also situations in which the marginal efficiency of capital does not
exist. Therefore, the marginal efficiency of capital cannot be the basis
of a general theory of investment.
(6) The marginal efficiency of capital favors small, short-term
projects. Alchian (p. 941) and Solomon (p. 126) show that MEC
calculations assume that the project's cash flows are reinvested at
the marginal efficiency of capital. In contrast, NPV calculations assume
that the project's cash flows are reinvested at the interest rate.
The marginal efficiency of capital's reinvestment rate assumption
penalizes large, long-term investment projects.
(7) The Keynesian liquidity preference theory of the yield curve is
incompatible with the marginal efficiency of capital. The marginal
efficiency of capital requires that all cash flows are discounted at the
same rate, while the liquidity preference theory of the yield curve
requires that each cash flow is discounted at a different rate depending
on the time to maturity.
(8) The loanable funds market must be in equilibrium for the goods
market to be in equilibrium. The double disequilibrium created in the
loanable funds market by central bank loan expansion means the goods
market cannot be in equilibrium either. One problem with the Keynesian
IS-LM model is that it does not depict the double disequilibrium in the
loanable funds market created by central bank loan expansion.
Edward W. Fuller (Edward.W.Fuller@gmail.com), MBA, is a research
consultant at SIG.
The author thanks an anonymous referee for helpful comments. All
errors are the author's responsibility.
Table 1. NPV of Wooden Bridge at 10% Interest Rate
Time Cash Flow Discounted Cash Flow
0 -2,000 -2,000
1 1,000 909.09
2 1,000 826.45
3 1,000 751.31
Present Value 2,486.85
Net Present Value 486.85
Table 2. NPV of Wooden Bridge at 5% Interest Rate
Time Cash Flow Discounted Cash Flow
0 -2,000 -2,000
1 1,000 952.38
2 1,000 907.03
3 1,000 863.84
Present Value 2,723.25
Net Present Value 723.25
Table 3. Wooden Bridge NPV Schedule
Interest Rate Wooden Bridge
1% 940.99
2% 883.88
3% 828.61
4% 775.09
5% 723.25
6% 673.01
7% 624.32
8% 577.10
9% 531.29
10% 486.85
Table 4. NPV of Steel Bridge at 10% Interest Rate
Time Cash Flow Discounted Cash Flow
0 -5,000 -5,000
1 0 0
2 0 0
3 1,000 751.31
4 1,000 683.01
5 1,000 620.92
6 1,000 564.47
7 1,000 513.16
8 1,000 466.51
9 1,000 424.10
10 1,000 385.54
Present Value 4,409.03
Net Present Value -590.97
Table 5. Wooden and Steel Bridge NPV Schedule
Interest Rate Wooden Bridge Steel Bridge
1% 940.99 2,500.91
2% 883.88 2,041.02
3% 828.61 1,616.73
4% 775.09 1,224.80
5% 723.25 862.32
5.48% 699.10 699.10
6% 673.01 526.69
7% 624.32 215.56
7.74% 589.26 0.00
8% 577.10 -73.18
9% 531.29 -341.45
10% 486.85 -590.97
23.38% 0.00 -2,713.02
Table 6. Marginal Efficiency of Capital
Time Cash Flow Discounted Cash Flow
0 -2,000 -2,000
1 1,000 810.54
2 1,000 656.97
3 1,000 532.50
Present Value 2,000
Net Present Value 0
MEC 23.38%
Table 7. NPV Schedule with MEC
Interest Rate Wooden Bridge
1% 940.99
2% 883.88
3% 828.61
4% 775.09
5% 723.25
6% 673.01
7% 624.32
8% 577.10
9% 531.29
10% 486.85
23.38% 0.00
Table 8. Collapse of MEC
Time Cash Flow Discounted Cash Flow
0 -2,000 -2,000
1 750 706.69
2 750 665.88
3 750 627.43
Present Value 2,000
Net Present Value 0
MEC 6.13%