ECON1102 Lecture Notes - Lecture 10: Real Interest Rate, Aggregate Demand, Best Response
10 – Aggregate Demand and Aggregate Supply
PAE and real interest rate
• In income-expenditure model, PAE depends on level of real output
Want to allow for the real interest rate to influence PAE
• Two main channels:
1. Higher real interest rates will lead households to increase saving and defer
current consumption
2. Higher real interest rates will raise the cost of capital and reduce business
investment
Model for PAE
• Consumption: C = C0 + c (Y – T) – r
• Investment: IP = I0 – ßr
(–) is negative effect from real interest rate
Assume > 0 and ß > 0 are some positive numbers
• PAE = [C0 – cT0 + I0 + G0 + X0] – ( + ß)r + (c (1 – t) – m)Y
PAE depends (negatively) on real interest rate
For any given output level, PAE will fall with an increase in the real interest rate
If we assume that the RBA can set the real interest rate, then we have a
mechanism by which monetary policy can affect PAE and equilibrium output
• Y = PAE:
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2
• Mechanism by which monetary policy can affect real GDP
Policy reaction function
• r = r0 + yπ
y > 0 captures the (endogenous) response of the RBA to inflation
r0 represents factors – other than inflation rate – that might influence real policy
rate
(a) Changes in r0 reflect discretionary changes in monetary policy
Aggregate demand (AD) curve
• A PAE curve that depends on the real interest rate
• A policy reaction function for the RBA, in which the real interest rate responds to the
inflation rate
• PAE curve & PRF → AD curve
Link output Y and inflation π
• Simplifying:
Let k =
• Model implies a negative relationship between equilibrium output and rate of
inflation
AD curve has a negative slope
• Other things equal, an increase in inflation is associated with a fall in equilibrium
output
• Model explains negative slope as reflecting behaviour of central bank
• When inflation is high, RBA will raise real interest rate
Increase in r reduces consumption and investment (i.e. PAE) and this produces a
fall in equilibrium output
• Other reasons not explicitly stated in model: wealth, distributional and uncertainty
effects
Shifts in AD curve
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3
• Exogenous changes in spending or taxes
Fiscal policy, private spending
• Eogenous change in RBA’s polic reaction function, r0
Increase in r0 produces an upward shift in the PRF (tighter monetary policy) and
leads to inward shift in AD curve
Aggregate supply – how does inflation change with aggregate production?
• Expected rate of inflation
Assume expected & actual inflation is sticky or slow to adjust in the short-run
(a) Consistent with observed persistence in inflation rates
i. Actual = expected inflation: π = πe
ii. Adaptive expectations: πe = π-1
iii. Actual inflation: π = π-1
(b) Inflation is constant (fixed or sticky) in short-run
• Aggregate shocks to business production costs
Introduce one-period shocks to inflation rate (e.g. indirect tax changes or
changes in energy prices)
π = π-1 +
(a) > 0 = adverse or unfavourable shock
(b) < 0 = favourable shock
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Document Summary
In income-expenditure model, pae depends on level of real output. Model for pae: consumption: c = c0 + c (y t) r. ( ) is negative effect from real interest rate. Assume > 0 and > 0 are some positive numbers: pae = [c0 ct0 + i0 + g0 + x0] ( + )r + (c (1 t) m)y. Pae depends (negatively) on real interest rate. For any given output level, pae will fall with an increase in the real interest rate. Policy reaction function r = r0 + y . Y > 0 captures the (endogenous) response of the rba to inflation. R0 represents factors other than inflation rate that might influence real policy rate (a) changes in r0 reflect discretionary changes in monetary policy. Link output (cid:894)y(cid:895) and inflation (cid:894) (cid:895: simplifying: Let k : model implies a negative relationship between equilibrium output and rate of inflation.