0. A closed economy, market-clearing model
Outline of model
A closed economy, market-clearing model
Supply side
factor markets (supply, demand, price)
determination of output/income
Demand side
determinants of C, I, and G
Equilibrium
goods market
loanable funds market
DONE 
DONE 
Next 
We’ve now completed the supply side of the model.

1. Demand for goods & services
Components of aggregate demand:
C = consumer demand for g & s
I = demand for investment goods
G = government demand for g & s
(closed economy: no NX )
“g & s” is short for “goods & services”

2. Consumption, C
def: Disposable income is total income minus total taxes: Y – T.
Consumption function: C = C (Y – T )
Shows that (Y – T )  C
def: Marginal propensity to consume (MPC) is the change in C when disposable income increases by one dollar.
Again, we are using the short-hand notation that will appear throughout the remaining PowerPoints:
X  Y means “an increase in X causes a decrease in Y.”

3. The consumption function
Y – T
C (Y –T )
The slope of the consumption function is the MPC.
MPC 1

4. Investment, I The investment function is I = I (r ),
where r denotes the real interest rate, the nominal interest rate corrected for inflation.
The real interest rate is
the cost of borrowing
the opportunity cost of using one’s own funds to finance investment spending
So, r  I

5. The investment functionr I
Spending on investment goods depends negatively on the real interest rate.
I (r )

6. Government spending, G G = Govt spending on goods and services.
G excludes transfer payments (e.g., social security benefits, unemployment insurance benefits).
Assume government spending and total taxes are exogenous:

7. The market for goods & services
Aggregate demand:
Aggregate supply:
Equilibrium:
The real interest rate adjusts to equate demand with supply.
In the equation for the equilibrium condition, note that the real interest rate is the only variable that doesn’t have a “bar” over it – it’s the only endogenous variable in the equation, and it adjusts to equate the demand and supply in the goods market.
note that the interest rate is important in financial markets as well, so we will next develop a simple model of the financial system.

8. The loanable funds market
A simple supply-demand model of the financial system.
One asset: “loanable funds”
demand for funds: investment
supply of funds: saving
“price” of funds: real interest rate

9. Demand for funds: Investment
The demand for loanable funds…
comes from investment: Firms borrow to finance spending on plant & equipment, new office buildings, etc. Consumers borrow to buy new houses.
depends negatively on r, the “price” of loanable funds (cost of borrowing).

10. Loanable funds demand curveI
The investment curve is also the demand curve for loanable funds.
I (r )

11. Supply of funds: Saving
The supply of loanable funds comes from saving:
Households use their saving to make bank deposits, purchase bonds and other assets. These funds become available to firms to borrow to finance investment spending.
The government may also contribute to saving if it does not spend all the tax revenue it receives.

12. Types of saving private saving = (Y – T ) – C public saving = T – G
national saving, S
= private saving + public saving
= (Y –T ) – C T – G
= Y – C – G
Suppose a person earns $50,000/year, pays $10,000 in taxes, and spends $35,000 on goods and services. There’s $5000 remaining. What happens to that $5000? The person might use it to buy stocks or bonds, or she might put it in her savings account or money market deposit account. In all of these cases, this $5000 becomes part of the supply of loanable funds in the financial system.
public saving is tax revenue minus government spending.
Notice the analogy to private saving – both concepts represent income less spending: for the private household, income is (Y-T) and spending is C. For the government, income is T and spending is G.

13. Notation:  = change in a variable
For any variable X, X = “the change in X ”
 is the Greek (uppercase) letter Delta
Examples:
If L = 1 and K = 0, then Y = MPL.
More generally, if K = 0, then
X is (practically) the same thing as dX (if X is small). Furthermore, some basic rules from calculus apply here with s:
The derivative of a sum is the sum of the derivatives: (X+Y) = X + Y
The product rule: XY = (X)(Y) + (X)(Y)
In fact, you can derive the two arithmetic tricks for working with percentage changes presented in chapter 2.
Just take the preceding expression for the product rule and divide through by XY to get (XY)/XY = X/X + Y/Y, the first of the two arithmetic tricks.
(YT ) = Y  T , so
C = MPC  (Y  T )
= MPC Y  MPC T

14. For each of the following, compute S :
NOW YOU TRY: Saving
Suppose MPC = 0.8 and MPL = 20.
For each of the following, compute S :
a. G = 100
b. T = 100
c. Y = 100
d. L = 10

15. Budget surpluses and deficits
If T > G, budget surplus = (T – G ) = public saving.
If T < G, budget deficit = (G – T ) and public saving is negative.
If T = G , “balanced budget,” public saving = 0.
The U.S. government finances its deficit by issuing Treasury bonds – i.e., borrowing.

16. U.S. Federal Government Surplus/Deficit, 1940-2009 and estimates for 2010-2015
percent of GDP
Notes:
1. The huge deficit in the early 1940s was due to WW2. Wars are expensive.
2. The budget is closed to balanced in the ’50s and ’60s, and begins a downward trend in the ’70s.
3. The early ’80s saw the largest deficits (as % of GDP) of the post-WW2 era, due to the Reagan tax cuts, defense buildup, and growth in entitlement program outlays.
4. The budget begins a positive trend in the early 1990s, and a surplus emerges in the late 1990s. There are several possible explanations for the improvement. First, President Bush (the first one) broke his campaign promise not to raise taxes. Second, the Clinton administration barely squeaked a deficit reduction deal through Congress (with Al Gore casting the tie-breaking vote in the Senate). And third, and probably most important, there was a swelling of tax revenues due to the surge in economic growth and the stock market boom. (A stock market boom leads to large capital gains, which leads to large revenues from the capital gains tax.)
5. The budget swings to deficit again in 2001, due to the Bush tax cuts and a recession.
6. Recently, the budget deficit in current dollars has reached all-time highs, due to a sharp fall tax receipts, the enactment of multi-billion dollar bailouts and a large stimulus package.
data source:
Budget of the United States Government: Historical Tables Fiscal Year 2011, Table 1.2

17. U.S. Federal Government Debt, 1940-2009 and estimates for 2010-2015
percent of GDP
government finances its deficits by borrowing from the public. (This borrowing takes the form of selling Treasury bonds). Persistent deficits over time imply persistent borrowing, which causes the debt to increase.
After WW2, occasional budget surpluses allowed the government to retire some of its WW2 debt; also, normal economic growth increased the denominator of the debt-to-GDP ratio. Starting in the early 1980s, corresponding to the beginning of huge and persistent deficits, we see a huge increase in the debt-to-GDP ratio, from 32% in 1981 to 66% in In the mid 1990s, budget surpluses and rapid growth started to reduce the debt-to-GDP ratio, but it started rising again in 2001 due to the economic slowdown, the Bush tax cuts, and higher spending (Afghanistan & Iraq, war on terrorism, 2002 airline bailout, etc).
The current financial crisis / recession will surely boost the debt ratio, as revenues have fallen while outlays (the stimulus package, bailouts) have sharply increased. The data shown end in 2007, and we are just beginning to see a rise in the debt ratio that will surely accelerate through 2010 and perhaps beyond.
source:
Budget of the United States Government: Historical Tables Fiscal Year 2011 Table 7.1

18. Loanable funds supply curve
S, I
National saving does not depend on r, so the supply curve is vertical.
At the end of this chapter, we will briefly consider how things would be different if Consumption (and therefore Saving) were allowed to depend on the interest rate.
For now, though, they do not.

19. Loanable funds market equilibrium
S, I
I (r )
Equilibrium real interest rate
Equilibrium level of investment

20. The special role of r Eq’m in L.F. market Eq’m in goods market
r adjusts to equilibrate the goods market and the loanable funds market simultaneously:
If L.F. market in equilibrium, then
Y – C – G = I
Add (C +G ) to both sides to get
Y = C + I + G (goods market eq’m)
Thus,
This slide establishes that we can use the loanable funds supply/demand diagram to see how the interest rate that clears the goods market is determined.
the symbol  means each one implies the other. The thing on the left implies the thing on the right, and vice versa.
More short-hand: “eq’m” is short for “equilibrium” and “LF” for “loanable funds.”
Eq’m in L.F. market
Eq’m in goods market

21. Digression: Mastering models
To master a model, be sure to know:
1. Which of its variables are endogenous and which are exogenous.
2. For each curve in the diagram, know:
a. definition
b. intuition for slope
c. all the things that can shift the curve
3. Use the model to analyze the effects of each item in 2c.

22. Mastering the loanable funds model
Things that shift the saving curve
public saving
fiscal policy: changes in G or T
private saving
preferences
tax laws that affect saving
401(k)
IRA
replace income tax with consumption tax
Continuing from the previous slide, let’s look at all the things that affect the S curve. Then, we will pick one of those things and use the model to analyze its effects on the endogenous variables. Then, we’ll do the same for the I curve.

23. CASE STUDY: The Reagan deficits
Reagan policies during early 1980s:
increases in defense spending: G > 0
big tax cuts: T < 0
Both policies reduce national saving:

24. CASE STUDY: The Reagan deficits
1. The increase in the deficit reduces saving… r
S, I
I (r ) r2
2. …which causes the real interest rate to rise… r1
3. …which reduces the level of investment. I2 I1

25. Are the data consistent with these results?
variable 1970s 1980s
T – G –2.2 –3.9 S r I
The model says that investment should have fallen as much as savings. Why?
Answer: in our closed economy model of chapter 3, the only source of loanable funds is national saving. But the U.S. is actually an open economy. In the face of a fall in national saving (i.e. the domestic supply of loanable funds), firms can finance their investment spending by importing foreign loanable funds. More on this in an upcoming chapter.
T–G, S, and I are expressed as a percent of GDP
All figures are averages over the decade shown.

26. Mastering the loanable funds model, continued
Things that shift the investment curve:
some technological innovations
to take advantage some innovations, firms must buy new investment goods
tax laws that affect investment
e.g., investment tax credit

27. An increase in investment demand
S, I I2 I1
…raises the interest rate.
An increase in desired investment… r2 r1
But the equilibrium level of investment cannot increase because the supply of loanable funds is fixed.

28. Saving and the interest rate
Why might saving depend on r ?
How would the results of an increase in investment demand be different?
Would r rise as much?
Would the equilibrium value of I change?
Reasons why saving might depend on r:
An increase in r makes saving more attractive , increases the reward for postponing consumption
Many consumers finance their spending on big-ticket items like cars and furniture, and an increase in r makes such borrowing more expensive.
However, an increase in r might also reduce saving through the income effect: a higher interest rate makes net savers better off, so they purchase more of all “normal” goods. If current consumption is a normal good, then it will rise and saving will fall. It is usually assumed that the substitution effect is at least as great as the income effect, so that an increase in the interest rate will either increase saving or leave saving unchanged.

29. An increase in investment demand when saving depends on r
S, I
An increase in investment demand raises r,
which induces an increase in the quantity of saving,
which allows I to increase.
I(r)2
I(r) r2 I2 r1
When saving depends on the interest rate, an increase in investment demand causes the equilibrium values of saving and investment to rise, and causes the interest rate to rise – but not as much as when saving doesn’t depend on the interest rate. I1

30. CHAPTER SUMMARY Total output is determined by:
the economy’s quantities of capital and labor
the level of technology
Competitive firms hire each factor until its marginal product equals its price.
If the production function has constant returns to scale, then labor income plus capital income equals total income (output).

31. CHAPTER SUMMARY A closed economy’s output is used for:
consumption
investment
government spending
The real interest rate adjusts to equate the demand for and supply of:
goods and services
loanable funds

32. CHAPTER SUMMARY
A decrease in national saving causes the interest rate to rise and investment to fall.
An increase in investment demand causes the interest rate to rise, but does not affect the equilibrium level of investment if the supply of loanable funds is fixed.