How to Solve: IB Economics – Macroeconomic Equilibrium & AD/AS Diagrams (Keynesian vs Neoclassical)

How to Solve: IB Economics – Macroeconomic Equilibrium & AD/AS Diagrams (Keynesian vs Neoclassical)

Introduction

"Mastering AD/AS diagrams unlocks 15–20% of your IB Economics Paper 1 marks—and helps you explain real-world crises like recessions or inflation. One diagram, two schools of thought: Keynesian vs Neoclassical. Get this right, and you’ll ace short-answer questions, essays, and even data-response tasks."

What You Need To Know First

1. Aggregate Demand (AD): Total spending in an economy (C + I + G + (X−M)).
2. Aggregate Supply (AS): Total output firms produce at different price levels.
3. Equilibrium: Where AD = AS, determining real GDP and the price level.

(If you’re shaky on these, pause and review before continuing.)

KEY TERMS & FORMULAS

Key Terms

Formulas

1. AD Formula (Given on exam sheet) [ AD = C + I + G + (X - M) ]
2. C = Consumption
3. I = Investment
4. G = Government spending
5. X = Exports

6. M = Imports

7. Multiplier Effect (Given on exam sheet) [ k = \frac{1}{1 - MPC} \quad \text{or} \quad k = \frac{1}{MPS + MPT + MPM} ]

8. k = Multiplier
9. MPC = Marginal Propensity to Consume
10. MPS = Marginal Propensity to Save
11. MPT = Marginal Propensity to Tax
12. MPM = Marginal Propensity to Import

Step-by-Step Method

Step 1: Identify the School of Thought

• Keynesian: AS is horizontal at low output, then upward-sloping. Government intervention needed.
• Neoclassical: AS is vertical in the long run. Economy self-corrects; no need for intervention.

Step 2: Draw the Axes

• X-axis: Real GDP (output).
• Y-axis: Price Level (PL).

Step 3: Plot AD

• Draw a downward-sloping AD curve.
• Label it AD.

Step 4: Plot AS Based on School of Thought

• Keynesian:
• Draw a horizontal line at low output (sticky wages/prices).
• Then, an upward-sloping curve as output rises.
• Label it Keynesian AS.
• Neoclassical:
• Draw a vertical LRAS at full employment (potential output).
• Label it LRAS.

Step 5: Find Equilibrium

• Where AD intersects AS:
• Keynesian: May be below full employment (deflationary gap).
• Neoclassical: Always at full employment (vertical LRAS).

Step 6: Analyze Shifts

• AD Shifts: Caused by changes in C, I, G, or (X−M).
• Right shift → Higher PL and GDP (inflationary pressure).
• Left shift → Lower PL and GDP (recession).
• AS Shifts:
• Keynesian: Supply-side policies (e.g., education, tech) shift AS right.
• Neoclassical: LRAS shifts right with productivity gains (e.g., better tech, more capital).

Step 7: Identify Gaps

• Inflationary Gap: AD > LRAS (economy overheating).
• Deflationary Gap: AD < LRAS (unemployment above natural rate).

Step 8: Policy Implications

• Keynesian: Government should use fiscal policy (e.g., increase G) to close gaps.
• Neoclassical: No intervention needed; wages/prices adjust automatically.

Worked Examples

Example 1 – Basic (Keynesian Equilibrium)

Question: Draw a Keynesian AD/AS diagram showing a deflationary gap. Explain how fiscal policy can close it.

Steps:
1. Draw axes: X = Real GDP, Y = Price Level.
2. Draw downward-sloping AD.
3. Draw Keynesian AS: horizontal at low output, then upward-sloping.
4. Label equilibrium where AD = AS (below full employment).
5. Show deflationary gap (distance between equilibrium and full employment).
6. Shift AD right (e.g., increase G) to close the gap.

What we did and why: - Used Keynesian AS to show sticky wages/prices. - Fiscal policy (increase G) shifts AD right, closing the deflationary gap.

Example 2 – Medium (Neoclassical Equilibrium)

Question: Draw a Neoclassical AD/AS diagram showing an inflationary gap. Explain why no government intervention is needed.

Steps:
1. Draw axes: X = Real GDP, Y = Price Level.
2. Draw downward-sloping AD.
3. Draw vertical LRAS at full employment.
4. Shift AD right (e.g., increase C) to create an inflationary gap.
5. Show that wages/prices rise, shifting SRAS left until equilibrium returns to LRAS.

What we did and why: - Used Neoclassical LRAS to show flexible wages/prices. - No intervention needed because the economy self-corrects.

Example 3 – Exam-Style (Data Response)

Question: The government increases spending by $100 billion. MPC = 0.8. Calculate the final impact on GDP using the multiplier. Then, draw a Keynesian AD/AS diagram to show the effect.

Steps:
1. Calculate multiplier: [ k = \frac{1}{1 - MPC} = \frac{1}{1 - 0.8} = 5 ]
2. Final impact on GDP: [ \Delta GDP = k \times \Delta G = 5 \times 100 = 500 \text{ billion} ]
3. Draw Keynesian AD/AS diagram: - Shift AD right by $500 billion. - Show new equilibrium at higher GDP (may still be below full employment).

What we did and why: - Used the multiplier to calculate the total impact of government spending. - Keynesian diagram shows how fiscal policy increases output.

Common Mistakes

Exam Traps

1-Minute Recap

"Here’s the night-before cheat sheet:
1. Keynesian AS: Horizontal at low output, then upward-sloping. Government intervention needed.
2. Neoclassical AS: Vertical LRAS. Economy self-corrects.
3. AD shifts: C, I, G, (X−M). Right = inflationary, left = deflationary.
4. AS shifts: Productivity, costs. Right = growth, left = recession.
5. Gaps: Inflationary (AD > LRAS), deflationary (AD < LRAS).
6. Diagrams: Always label axes, curves, and equilibrium.
7. Policies: Keynesian = fiscal, Neoclassical = no intervention.

Draw the diagram, explain the shift, and link to real-world outcomes. You’ve got this!