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# MACROECONOMICS-CH10

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• This chapter sets up the IS-LM model, which chapter 11 then uses extensively to analyze the effects of policies and economic shocks. This chapter also introduces students to the Keynesian Cross and Liquidity Preference models, which underlie the IS curve and LM curve, respectively. If you would like to spend less time on this chapter, you might consider omitting the Keynesian Cross, instead using the loanable funds model from Chapter 3 to derive the IS curve. Advantage: students are already familiar with the loanable funds model, so skipping the KC means one less model to learn. Additionally, the KC model is not used anywhere else in this textbook. Once it’s used to derive IS, it disappears for good. However, there are some good reasons for NOT omitting the KC model: 1) Many principles textbooks (though not Mankiw’s) cover the KC model; students who learned the KC model in their principles class may benefit from seeing it here, as a bridge to new material (the IS curve). 2) The KC model has historical value. One could argue that somebody graduating from college with a degree in economics should be familiar with the KC model.
• ### Transcript

• 1.
• 2. In this chapter you will learn
• the IS curve, and its relation to
• the Keynesian Cross
• the Loanable Funds model
• the LM curve, and its relation to
• the Theory of Liquidity Preference
• how the IS-LM model determines income and the interest rate in the short run when P is fixed
• 3. Context
• Chapter 9 introduced the model of aggregate demand and aggregate supply.
• Long run
• prices flexible
• output determined by factors of production & technology
• unemployment equals its natural rate
• Short run
• prices fixed
• output determined by aggregate demand
• unemployment is negatively related to output
• 4. Context
• This chapter develops the IS-LM model, the theory that yields the aggregate demand curve.
• We focus on the short run and assume the price level is fixed.
• 5. The Keynesian Cross
• A simple closed economy model in which income is determined by expenditure. (due to J.M. Keynes)
• Notation:
• I = planned investment
• E = C + I + G = planned expenditure
• Y = real GDP = actual expenditure
• Difference between actual & planned expenditure: unplanned inventory investment
• 6. Elements of the Keynesian Cross consumption function: for now, investment is exogenous: planned expenditure: Equilibrium condition: govt policy variables:
• 7. Graphing planned expenditure income, output, Y E planned expenditure E = C + I + G MPC 1
• 8. Graphing the equilibrium condition income, output, Y E planned expenditure 45 º E = Y
• 9. The equilibrium value of income income, output, Y E planned expenditure E = Y E = C + I + G Equilibrium income
• 10. An increase in government purchases E = Y … so firms increase output, and income rises toward a new equilibrium Y E E = C + I + G 1 E 1 = Y 1 E = C + I + G 2 E 2 = Y 2  Y At Y 1 , there is now an unplanned drop in inventory…  G
• 11. Solving for  Y equilibrium condition in changes because I exogenous because  C = MPC  Y Collect terms with  Y on the left side of the equals sign: Finally, solve for  Y :
• 12. The government purchases multiplier
• Example: MPC = 0.8
The increase in G causes income to increase by 5 times as much!
• 13. The government purchases multiplier
• Definition: the increase in income resulting from a \$1 increase in G .
• In this model, the G multiplier equals
In the example with MPC = 0.8,
• 14. Why the multiplier is greater than 1
• Initially, the increase in G causes an equal increase in Y :  Y =  G .
• But  Y   C
•  further  Y
•  further  C
•  further  Y
• So the final impact on income is much bigger than the initial  G .
• 15. An increase in taxes … so firms reduce output, and income falls toward a new equilibrium Initially, the tax increase reduces consumption, and therefore E : Y E E = Y E = C 2 + I + G E 2 = Y 2 E = C 1 + I + G E 1 = Y 1  Y At Y 1 , there is now an unplanned inventory buildup…  C =  MPC  T
• 16. Solving for  Y eq’m condition in changes I and G exogenous Solving for  Y : Final result:
• 17. The Tax Multiplier
• def: the change in income resulting from a \$1 increase in T :
If MPC = 0.8, then the tax multiplier equals
• 18. The Tax Multiplier
• … is negative : A tax hike reduces consumer spending, which reduces income.
• … is greater than one ( in absolute value ) : A change in taxes has a multiplier effect on income.
• … is smaller than the govt spending multiplier : Consumers save the fraction (1-MPC) of a tax cut, so the initial boost in spending from a tax cut is smaller than from an equal increase in G .
• 19. The Tax Multiplier
• … is negative : An increase in taxes reduces consumer spending, which reduces equilibrium income.
• … is greater than one ( in absolute value ) : A change in taxes has a multiplier effect on income.
• … is smaller than the govt spending multiplier : Consumers save the fraction (1-MPC) of a tax cut, so the initial boost in spending from a tax cut is smaller than from an equal increase in G .
• 20. Exercise:
• Use a graph of the Keynesian Cross to show the impact of an increase in investment on the equilibrium level of income/output.
• 21. The IS curve
• def: a graph of all combinations of r and Y that result in goods market equilibrium,
• i.e. actual expenditure (output) = planned expenditure
• The equation for the IS curve is:
• 22. Deriving the IS curve
•  r   I
Y 2 Y 1 Y 2 Y 1 E = C + I ( r 1 )+ G E = C + I ( r 2 )+ G r 1 r 2 E = Y IS   E   Y Y E r Y  I
• 23. Understanding the IS curve’s slope
• The IS curve is negatively sloped.
• Intuition: A fall in the interest rate motivates firms to increase investment spending, which drives up total planned spending ( E ).
• To restore equilibrium in the goods market, output (a.k.a. actual expenditure, Y ) must increase.
• 24. The IS curve and the Loanable Funds model r 1 r 2 r 1 r 2 (a) The L.F. model (b) The IS curve IS S , I r I ( r ) r Y Y 1 Y 2 S 1 S 2
• 25. Fiscal Policy and the IS curve
• We can use the IS-LM model to see how fiscal policy ( G and T ) can affect aggregate demand and output.
• Let’s start by using the Keynesian Cross to see how fiscal policy shifts the IS curve…
• 26. Shifting the IS curve:  G
• At any value of r ,  G   E   Y
Y 2 Y 1 Y 2 Y 1 E = C + I ( r 1 )+ G 1 E = C + I ( r 1 )+ G 2 r 1 E = Y IS 1 The horizontal distance of the IS shift equals IS 2 … so the IS curve shifts to the right. Y E r Y  Y
• 27. Exercise: Shifting the IS curve
• Use the diagram of the Keynesian Cross or Loanable Funds model to show how an increase in taxes shifts the IS curve.
• 28. The Theory of Liquidity Preference
• due to John Maynard Keynes.
• A simple theory in which the interest rate is determined by money supply and money demand.
• 29. Money Supply
• The supply of real money balances is fixed:
M/P real money balances r interest rate
• 30. Money Demand
• Demand for real money balances:
M/P real money balances r interest rate L ( r )
• 31. Equilibrium
• The interest rate adjusts to equate the supply and demand for money:
M/P real money balances r interest rate L ( r ) r 1
• 32. How the Fed raises the interest rate
• To increase r , Fed reduces M
M/P real money balances r interest rate L ( r ) r 1 r 2
• 33. CASE STUDY Volcker’s Monetary Tightening
• Late 1970s:  > 10%
• Oct 1979: Fed Chairman Paul Volcker announced that monetary policy would aim to reduce inflation.
• Aug 1979-April 1980: Fed reduces M / P 8.0%
• Jan 1983:  = 3.7%
How do you think this policy change would affect interest rates?
• 34. Volcker’s Monetary Tightening, cont.  i < 0  i > 0 1/1983: i = 8.2% 8/1979: i = 10.4% 4/1980: i = 15.8% flexible sticky Quantity Theory, Fisher Effect (Classical) Liquidity Preference (Keynesian) prediction actual outcome The effects of a monetary tightening on nominal interest rates prices model long run short run
• 35. The LM curve
• Now let’s put Y back into the money demand function:
The LM curve is a graph of all combinations of r and Y that equate the supply and demand for real money balances. The equation for the LM curve is:
• 36. Deriving the LM curve r 1 r 2 r 1 r 2 (a) The market for real money balances (b) The LM curve M/P r L ( r , Y 1 ) r Y Y 1 L ( r , Y 2 ) Y 2 LM
• 37. Understanding the LM curve’s slope
• The LM curve is positively sloped.
• Intuition: An increase in income raises money demand.
• Since the supply of real balances is fixed, there is now excess demand in the money market at the initial interest rate.
• The interest rate must rise to restore equilibrium in the money market.
• 38. How  M shifts the LM curve r 1 r 2 r 1 r 2 (a) The market for real money balances (b) The LM curve M/P r L ( r , Y 1 ) r Y Y 1 LM 1 LM 2
• 39. Exercise: Shifting the LM curve
• Suppose a wave of credit card fraud causes consumers to use cash more frequently in transactions.
• Use the Liquidity Preference model to show how these events shift the LM curve.
• 40. The short-run equilibrium
• The short-run equilibrium is the combination of r and Y that simultaneously satisfies the equilibrium conditions in the goods & money markets:
Equilibrium interest rate Equilibrium level of income Y r IS LM
• 41. The Big Picture Keynesian Cross Theory of Liquidity Preference IS curve LM curve IS-LM model Agg. demand curve Agg. supply curve Model of Agg. Demand and Agg. Supply Explanation of short-run fluctuations
• 42. Chapter summary
• Keynesian Cross
• basic model of income determination
• takes fiscal policy & investment as exogenous
• fiscal policy has a multiplied impact on income.
• IS curve
• comes from Keynesian Cross when planned investment depends negatively on interest rate
• shows all combinations of r and Y that equate planned expenditure with actual expenditure on goods & services
• 43. Chapter summary
• Theory of Liquidity Preference
• basic model of interest rate determination
• takes money supply & price level as exogenous
• an increase in the money supply lowers the interest rate
• LM curve
• comes from Liquidity Preference Theory when money demand depends positively on income
• shows all combinations of r and Y that equate demand for real money balances with supply
• 44. Chapter summary
• IS-LM model
• Intersection of IS and LM curves shows the unique point ( Y , r ) that satisfies equilibrium in both the goods and money markets.
• 45. Preview of Chapter 11
• In Chapter 11, we will
• use the IS-LM model to analyze the impact of policies and shocks
• learn how the aggregate demand curve comes from IS-LM
• use the IS-LM and AD-AS models together to analyze the short-run and long-run effects of shocks
• learn about the Great Depression using our models
• 46.