macro CHAPTER TEN Aggregate Demand I macroeconomics fifth edition N. Gregory Mankiw PowerPoint Slides by Ron Cronovich 2002 Worth Publishers, all rights reserved
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 Aggregate Demand I slide 1
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 Aggregate Demand I slide 2
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. Aggregate Demand I slide 3
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 Aggregate Demand I slide 4
Elements of the Keynesian Cross consumption function: C = C( Y T ) govt policy variables: G = G, T = T for now, investment is exogenous: I = I planned expenditure: E = C( Y T ) + I + G Equilibrium condition: Actual expenditure = Planned expenditure Y = E Aggregate Demand I slide 5
Graphing planned expenditure E planned expenditure E =C +I +G 1 MPC income, output, Y Aggregate Demand I slide 6
Graphing the equilibrium condition E planned expenditure E =Y 45º income, output, Y Aggregate Demand I slide 7
The equilibrium value of income E planned expenditure E =Y E =C +I +G income, output, Y Equilibrium income Aggregate Demand I slide 8
An increase in government purchases At Y 1, there is now an unplanned drop in inventory E E =Y E =C +I +G 2 E =C +I +G 1 G so firms increase output, and income rises toward a new equilibrium E 1 = Y 1 Y E 2 = Y 2 Y Aggregate Demand I slide 9
Solving for Y Y = C + I + G equilibrium condition Y = C + I + G in changes = C + G because I exogenous = MPC Y + G because C = MPC Y Collect terms with Y on the left side of the equals sign: (1 MPC) Y = G Finally, solve for Y : 1 Y = G 1 MPC Aggregate Demand I slide 10
The government purchases multiplier Example: MPC = 0.8 1 Y = G 1 MPC 1 1 = G = G = 5 G 1 0. 8 0. 2 The increase in G causes income to increase by 5 times as much! Aggregate Demand I slide 11
The government purchases multiplier Definition: the increase in income resulting from a $1 increase in G. In this model, the G multiplier equals Y G = 1 1 MPC In the example with MPC = 0.8, Y G 1 = = 1 0.8 5 Aggregate Demand I slide 12
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. Aggregate Demand I slide 13
An increase in taxes Initially, the tax increase reduces consumption, and therefore E: E E =Y E =C 1 +I +G E =C 2 +I +G C = MPC T so firms reduce output, and income falls toward a new equilibrium E 2 = Y 2 Y At Y 1, there is now an unplanned inventory buildup E 1 = Y 1 Y Aggregate Demand I slide 14
Solving for Y Y = C + I + G = C eq m condition in changes I and G exogenous = MPC ( Y T ) Solving for Y : (1 MPC) Y = MPC T Final result: MPC Y = T 1 MPC Aggregate Demand I slide 15
The Tax Multiplier def: the change in income resulting from a $1 increase in T : Y T = MPC 1 MPC If MPC = 0.8, then the tax multiplier equals Y 08. 08. = = = T 1 0. 8 0. 2 4 Aggregate Demand I slide 16
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. Aggregate Demand I slide 17
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. Aggregate Demand I slide 18
Exercise: Use a graph of the Keynesian Cross to show the impact of an increase in investment on the equilibrium level of income/output. Aggregate Demand I slide 19
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: Y = CY ( T) + I( r) + G Aggregate Demand I slide 20
Deriving the IS curve E E =Y E =C +I (r 2 )+G r I E =C +I (r 1 )+G E I Y r Y 1 Y 2 Y r 1 r 2 Y 1 Y 2 IS Y Aggregate Demand I slide 21
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. Aggregate Demand I slide 22
The IS curve and the Loanable Funds model (a) The L.F. model (b) The IS curve r S 2 S 1 r r 2 r 2 r 1 I (r ) r 1 IS S, I Y 2 Y 1 Y Aggregate Demand I slide 23
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 Aggregate Demand I slide 24
Shifting the IS curve: GG At any value of r, G E Y so the IS curve shifts to the right. The horizontal distance of the IS shift equals 1 Y = G 1 MPC E r r 1 Y 1 Y 2 Y Y 1 Y 2 E =Y E =C +I (r 1 )+G 2 E =C +I (r 1 )+G 1 Y IS 1 IS 2 Y Aggregate Demand I slide 25
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. Aggregate Demand I slide 26
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. Aggregate Demand I slide 27
Money Supply The supply of real money balances is fixed: ( M P ) s = M P r interest rate ( M P ) s M P M/P real money balances Aggregate Demand I slide 28
Money Demand Demand for real money balances: d ( M P ) = L( r) r interest rate ( M P ) s L (r ) M P M/P real money balances Aggregate Demand I slide 29
The interest rate adjusts to equate the supply and demand for money: M P Equilibrium r interest rate r 1 ( M P ) s = L( r) L (r ) M P M/P real money balances Aggregate Demand I slide 30
How the Fed raises the interest rate To increase r, Fed reduces M r interest rate r 2 r 1 M 2 P M 1 P L (r ) M/P real money balances Aggregate Demand I slide 31
CASE STUDY Volcker s Monetary Tightening Late 1970s: π > 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: π = 3.7% How do do you think this policy change would affect interest rates? Aggregate Demand I slide 32
Volcker s Monetary Tightening, cont. The effects of a monetary tightening on nominal interest rates model prices prediction short run Liquidity Preference (Keynesian) sticky i > 0 long run Quantity Theory, Fisher Effect (Classical) flexible i < 0 actual outcome 8/1979: i = 10.4% 4/1980: i = 15.8% 1/1983: i = 8.2% Aggregate Demand I slide 33
The LM curve Now let s put Y back into the money demand function: ( M P ) d = L( r, Y ) 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: M P = L( r, Y ) Aggregate Demand I slide 34
Deriving the LM curve r (a) The market for real money balances r (b) The LM curve LM r 2 r 2 L (r,y 2 ) r 1 r 1 L (r,y 1 ) M 1 P M/P Y 1 Y 2 Y Aggregate Demand I slide 35
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. Aggregate Demand I slide 36
How M shifts the LM curve r (a) The market for real money balances r (b) The LM curve LM 2 r 2 r 2 LM 1 r 1 L (r,y 1 ) r 1 M 2 P M 1 P M/P Y 1 Y Aggregate Demand I slide 37
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. Aggregate Demand I slide 38
The short-run run equilibrium The short-run equilibrium is the combination of r and Y that simultaneously satisfies the equilibrium conditions in the goods & money markets: r LM Y = CY ( T) + I( r) + G M P = L( r, Y ) Equilibrium interest rate IS Equilibrium level of income Y Aggregate Demand I slide 39
The Big Picture Keynesian Cross Theory of Liquidity Preference IS curve LM curve IS-LM model Explanation of short-run fluctuations Agg. demand curve Agg. supply curve Model of Agg. Demand and Agg. Supply Aggregate Demand I slide 40
1. Keynesian Cross Chapter summary basic model of income determination takes fiscal policy & investment as exogenous fiscal policy has a multiplied impact on income. 2. 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 Aggregate Demand I slide 41
Chapter summary 3. 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 4. LM curve comes from Liquidity Preference Theory when money demand depends positively on income shows all combinations of r andy that equate demand for real money balances with supply Aggregate Demand I slide 42
5. IS-LM model Chapter summary Intersection of IS and LM curves shows the unique point (Y, r ) that satisfies equilibrium in both the goods and money markets. Aggregate Demand I slide 43
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 Aggregate Demand I slide 44
Aggregate Demand I slide 45