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The Production Possibilities Frontier. See pp. 32-38 in Case, Fair, and Oster’s Principles of Macroeconomics. Adapted from Time and Money: The Macroeconomics of Capital Structure by Roger W. Garrison London: Routledge, 2001. The Consumption-Investment Tradeoff

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slide1
The Production Possibilities Frontier

See pp. 32-38 in Case, Fair, and Oster’s

Principles of Macroeconomics

Adapted from Time and Money:

The Macroeconomics of Capital Structure

by Roger W. Garrison

London: Routledge, 2001

The Consumption-Investment Tradeoff

And the Essence of Economic Growth

2009

slide2
In any economy, some resources are devoted to producing consumables, the remaining resources being available for maintaining and expanding the economy’s productive capacity.

PRODUCTION POSSIBILITIES FRONTIER

CONSUMPTION

The Production Possibilities Frontier (PPF) depicts these alternatives during a given time period, typically one year.

INVESTMENT

The Production Possibilities Frontier

The tradeoff between CONSUMPTION (in the present) and INVESTMENT (for the future) should be an integral part of our macroeconomic thinking.

Under favorable conditions, a fully employed market economy allocates resources to both uses, making the most of the trade-off.

A “fully employed market economy” allows for a so-called “natural rate of unemployment,” which is about five or six percent. That is, frictional and structural unemployment are characteristic of even a healthy economy.

slide3
A PPF with heterogeneous

inputs

A PPF with homogeneous

inputs

If resources were characterized by perfect homogeneity, such that each unit of input is equally suitable for producing either kind of output (consumption goods or investment goods), then the PPF would be linear.

PRODUCTION POSSIBILITIES FRONTIER

PRODUCTION POSSIBILITIES FONTIER

CONSUMPTION

But raw materials and capital equipment are heterogeneous. Riverboats and river barges are not readily substitutable one for the other.

INVESTMENT

The heterogeneity of equipment and materials implies a convex PPF.

A riverboat isn’t very

suitable for carrying

industrial equipment.

As the tradeoff is made away from consumption and toward more investment, the scope for still more investment diminishes.

Microeconomists would describe this feature of the PPF in terms of a diminishing marginal rate of substitution.

A cruise on a river barge isn’t much fun.

slide4
“Investment” in this construction represents gross investment, which includes replacement capital.

CONSUMPTION

Typically, the investment needed just to replace worn out or obsolete capital is substantial but something less than gross investment.

INVESTMENT

Replacement

Capital

The extent to which gross investment exceeds the “replacement” magnitude constitutes net investment and allows for the expansion of the economy.

Net Investment

Gross

Investment

Positive net investment means that the economy is growing. The PPF shifts outward from year to year, permitting increasing levels of both consumption and investment.

This outward shifting of the PPF represents sustainable economic growth.

slide5
YEAR 0

YEAR 1

YEAR 2

YEAR 3

YEAR 4

Watch the economy grow.

Four periods of growth are shown—with consumption, as well as investment, increasing in each period.

The actual rate of expansion of the PPF depends upon many factors. For instance, with economic expansion, more resources are needed for capital replacement. And the desired trade-off between consuming and investing can itself change as the economy generates more wealth.

CONSUMPTION

INVESTMENT

Replacement

Capital

Net Investment

Gross

Investment

slide6
Watch the economy grow.

Four periods of growth are shown—with consumption, as well as investment, increasing in each period.

The actual rate of expansion of the PPF depends upon many factors. For instance, with economic expansion, more resources are needed for capital replacement. And the desired trade-off between consuming and investing can itself change as the economy generates more wealth.

CONSUMPTION

INVESTMENT

Watch the movement along the PPF.

Importantly, we note that forgoing some consumption with an eye toward consuming more in the future triggers a movement along the initial PPF and hence affects the rate at which the PPF expands outward.

slide7
Now watch the economy grow.

YEAR 0

YEAR 1

YEAR 2

YEAR 3

YEAR 4

CONSUMPTION

Increased thriftiness makes the difference.

Let’s compare the high-growth economy with the original low-growth economy.

INVESTMENT

slide8
CONSUMPTION

CONSUMPTION

INVESTMENT

INVESTMENT

Note the difference that an initial trading off of consumption for investment makes in the subsequent pattern of consumption and investment.

Without an initial increase in investment, consumption and investment increase modestly from period to period.

With an initial increase in investment at the expense of consumption, both consumption and investment increase dramatically from period to period.

By the fourth period, that initial increase in investment pays off as a higher level of consumption than would otherwise have been possible.

slide9
The time dimension is represented by the sequence of shifts of the PPF.

We can add to our understanding if we represent time explicitly on a horizontal axis and then keep track of consumption on the vertical axis.

CONSUMPTION

INVESTMENT

Explicitly tracking the level of consumption over time allows us to see that the tradeoff is essentially an intertemporal tradeoff.

In both representations, consumption is seen to fall as the economy is adapting to a higher growth rate, after which consumption rises more rapidly than before…

CONSUMPTION

Consumption in the present and near future is traded for consumption in the more distant future.

and eventually surpasses the old projected growth path.

TIME

slide10
There is nothing pre-ordained about the economy actually having a positive rate of growth.

YEAR 0

YEAR 1

YEAR 2

YEAR 3

YEAR 4

CONSUMPTION

Suppose that gross investment in the economy is just enough to replace worn out and obsolete capital—which means that net investment is zero.

The levels of consumption and (gross) investment would be maintained, but the economy would not grow.

INVESTMENT

Replacement

Capital

Net Investment = 0

Net Investment

Watch the economy not grow.

Gross

Investment

Gross

Investment

slide11
YEAR 0

YEAR 1

YEAR 2

YEAR 3

YEAR 4

In a no-growth economy (meaning no net investment), would it be possible for people to increase consumption?

CONSUMPTION

Yes, there is still some scope for movement along the PPF in the direction of more consumption and less investment.

INVESTMENT

Replacement

Capital

But what would be the consequences for the PPF in subsequent years?

Watch the economy experience negative growth, i.e., watch it contract.

Gross

Investment

Notice that consumption rises initially and then falls as the economy’s productive capacity diminishes over time.

slide12
As in the case of a clockwise movement along the PPF, we can add to our understanding of this counterclockwise movement by representing time explicitly on a horizontal axis and then keeping track of consumption on the vertical axis.

CONSUMPTION

INVESTMENT

In both representations, consumption is seen to rise as the economy is adapting to a negative growth rate, after which consumption declines—soon falling below the initial level.

The increase in consumption in the present and near future comes at the expense of a declining rate of consumption in the more distant future.

CONSUMPTION

TIME

slide13
CONSUMPTION

If gross investment exceeds replacement capital, the economy expands.

TIME

CONSUMPTION

If gross investment falls short of replacement capital, the economy contracts.

TIME

slide14
Consider two separate economies, one large and one small.

CONSUMPTION

Each PPF is broadly descriptive of two particular countries at the end of World War II.

On what basis can you make a prediction about the sizes of the two economies, say, two or three decades after the war?

INVESTMENT

Apart from their differing sizes, one possibly relevant difference is that the small country’s economy had been wrecked by bombing to a much greater extent than the large country’s economy.

Post-war United States

Japan grew much faster than the United States—not because it had been bombed, but because the consumption-investment tradeoff in post-war Japan was made in favor of a high level of investment.

In the United States, the tradeoff was made in the opposite direction by the consumption-oriented Americans.

CONSUMPTION

What two countries are these?

INVESTMENT

Post-war Japan

slide15
To this point, we’ve assumed that the economy is either on its PPF or is being expeditiously moved by market forces toward a point on its shifting PPF.

CONSUMPTION

Suppose, though, that during a given year, some market malfunction (or some perverse policy) takes the economy off its PPF.

INVESTMENT

If the economy is pushed beyond the PPF, its unemployment rate being driven below the 5-6 percent band, we say the economy is “overheated.”

Points very far beyond the PPF are simply out of reach (in real terms). Strong market forces pushing in this direction will impinge on prices rather than on quantities. The economy will experience price inflation.

And in extreme cases, it can experience hyper-inflation.

slide16
To this point, we’ve assumed that the economy is either on its PPF or is being expeditiously moved by market forces toward a point on its shifting PPF.

CONSUMPTION

Suppose, though, that during a given year, some market malfunction (or some perverse policy) takes the economy off its PPF.

INVESTMENT

If the economy is pushed beyond the PPF, its unemployment rate being driven below the 5-6 percent band, we say the economy is “overheated.”

Points very far beyond the PPF are simply out of reach (in real terms). Strong market forces pushing in this direction will impinge on prices rather than on quantities. The economy will experience price inflation.

And in extreme cases, it can experience hyper-inflation.

If the economy is pushed inside its PPF, its unemployment rate rising above the 5–6 percent band, we say that the economy is in a recession.

If the economy is pushed far inside its PPF for an extended period of time, we say that the economy is in a depression.

slide17
Notice that, together with the locus of the fully employed economy, the various possible market malfunctions (or consequences of perverse policy) are arrayed along a linear path:

CONSUMPTION

inflated

hyper-inflated

over-heated

fully employed

recessed

A depressed economy

A recessed economy

A fully employed economy

An over-heated economy

An inflated economy

A hyper-inflated economy

depressed

INVESTMENT

Economists who believe that “markets work” argue that market forces can move the economy along the PPF in response to changes in intertemporal preferences.

They argue that movements off the PPF are largely a consequence of perverse macroeconomic policy.

Economists who believe that the market economy is inherently flawed argue that market forces will move the economy along the linear path producing periodic bouts of unemployment and inflation.

They argue that “stimulus packages” and price controls are essential to the economy’s macroeconomic health.

What do you suppose is the significance of the straight line that passes through these points?

slide18
The Production Possibilities Frontier

Adapted from Time and Money:

The Macroeconomics of Capital Structure

by Roger W. Garrison

London: Routledge, 2001

The Consumption-Investment Tradeoff

And the Essence of Economic Growth

2009

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