AP Macroeconomics: Business Cycle (Phases: Expansion, Peak, Contraction/Recession, Trough)

AP Macroeconomics – Business Cycle (Phases: Expansion, Peak, Contraction/Recession, Trough)

AP Macroeconomics – Business Cycle Study Guide
(Expansion-Peak-Contraction/Recession-Trough)

What This Is

The business cycle describes the short?run fluctuations of real GDP and unemployment that an economy experiences as it moves through expansion, peak, contraction (recession), and trough. AP?Macroeconomics expects you to identify each phase on a graph, explain the underlying macro?policy forces, and predict how variables such as price level, output, and unemployment change. Real?world example: From 2010?2019 the U.S. economy expanded after the Great Recession, hit a peak in early?2020, then contracted sharply when COVID?19 shut down activity, creating a trough in mid?2020 before the next expansion began.

Key Terms & Formulas

• Business Cycle – The recurring pattern of expansion-peak-contraction-trough in real GDP and unemployment.
• Real GDP (Y) – Inflation?adjusted output; measured in constant dollars.
• Potential GDP (Y*) – The level of output the economy can produce when all resources are fully employed (the long?run aggregate?supply curve).
• Output Gap – (Y?Y*) / Y*; positive in expansion (inflationary gap), negative in contraction (recessionary gap).
• AD?AS Model (Aggregate?Demand/Aggregate?Supply) – Graph with price level (P) on the vertical axis and real GDP (Y) on the horizontal axis; AD slopes down, SR?AS slopes up, LR?AS is vertical at Y*.
• Phillips Curve (SR) – Shows the inverse short?run relationship between inflation (?) and unemployment (u); axes:? (vertical), u (horizontal).
• Fiscal Multiplier (k) – ?Y = k·?G (or k·?T); where k = 1 / (1?MPC) if the multiplier is based on government spending, MPC = marginal propensity to consume.
• Monetary Policy Transmission – ?i-?AD: A change in the federal funds rate (i) shifts the AD curve left (higher i) or right (lower i).
• Okun’s Law – ?u = –?·?Y%; a 1?% increase in real GDP reduces unemployment by roughly ?-0.5 percentage points.
• Recession Definition (NBER) – Two consecutive quarters of negative real GDP growth plus rising unemployment, falling industrial production, and declining retail sales.

Step?by?Step / Process Flow (Typical FRQ)

1. Identify the phase – Look at the given data (e.g., “real GDP grew 3?% last quarter, unemployment fell to 4?%”). Choose expansion, peak, contraction, or trough.
2. Draw the AD?AS diagram – Plot price level (P) on the vertical axis, real GDP (Y) on the horizontal axis. Sketch LR?AS vertical at Y*, then draw the current AD curve (label it AD?).
3. Show the shift – If the prompt mentions a policy change (e.g., “Fed cuts the discount rate”), shift AD right to AD? (expansion) or left to AD? (contraction).
4. Locate the new equilibrium – Mark the intersection of AD? with SR?AS; note the new price level (P?) and output (Y?).
5. Explain the macro?effects – State how the shift changes the output gap, inflation pressure, and unemployment (use Phillips Curve or Okun’s Law as needed).
6. Conclude with policy recommendation – Recommend fiscal or monetary tools to move the economy toward potential GDP (e.g., “increase G to raise AD, close the recessionary gap”).

Common Mistakes

• Mistake: Treating a change in price level as a shift of the SR?AS curve.
  Correction: A price?level change causes a movement along SR?AS; only changes in input prices, wages, or technology shift the curve.

• Mistake: Confusing peak with expansion and trough with contraction.
  Correction: The peak is the last point of expansion before AD starts to fall; the trough is the last point of contraction before AD begins to rise again.

• Mistake: Using the nominal GDP growth rate to label a recession.
  Correction: Recessions are defined by real GDP (inflation?adjusted) and accompanying labor?market indicators.

• Mistake: Assuming the fiscal multiplier is always >?1.
  Correction: The multiplier depends on the MPC and the openness of the economy; high imports or high taxes can reduce it below 1.

• Mistake: Forgetting that monetary policy shifts AD through interest rates, not directly through the money supply.
  Correction: On the AD?AS graph, a Fed rate cut-lower i-higher investment & consumption-AD shifts right.

AP Exam Insights

1. Graph?Only Questions – You’ll be asked to label the four phases on a single AD?AS diagram and to indicate the direction of the AD shift caused by a specific policy (e.g., “expansionary fiscal policy”).
2. FRQ Prompt Distinction – Many FRQs require you to compare two periods (e.g., “During Year?1 the economy was at a peak; during Year?2 it entered a recession”). Remember to state the phase first, then draw the appropriate graph.
3. Policy Tool Identification – The exam often tests whether you can match the tool to the desired effect: expansionary fiscal policy-increase G or cut taxes-AD right; contractionary monetary policy-raise the discount rate-AD left.
4. Quantitative Reasoning – You may need to calculate an output gap or apply Okun’s Law to estimate unemployment change. Keep the formulas handy and watch the sign (negative output gap-recession).

Quick Check Questions

1. Multiple?Choice:
   If the Fed raises the federal funds rate, which of the following occurs on the AD?AS diagram?
   Answer: AD shifts left (decrease).
   Explanation: Higher rates raise borrowing costs, reducing consumption and investment, so aggregate demand falls.

2. FRQ?Style (short answer):
   The economy is at a trough with real GDP 5?% below potential and unemployment 2?percentage points above the natural rate. Which policy would most quickly close the output gap, and why?
   Answer: Expansionary monetary policy (lower the discount rate) because it immediately reduces interest rates, boosts AD, and moves output toward potential.

3. Multiple?Choice:
   During an expansion, which of the following is most likely to increase?
   Answer: Inflation rate.
   Explanation: As AD shifts right, the price level rises, creating upward pressure on inflation.

Last?Minute Cram Sheet (10 One?Liners)

1. Business Cycle phases: Expansion-Peak-Contraction (Recession)-Trough.
2. AD?AS axes: P (vertical) vs. Y (horizontal).
3. Peak = last point of expansion; Trough = last point of contraction.
4. Fiscal multiplier = 1?/?(1?MPC).
5. Okun’s Law: ?u0.5·?Y% (approx.).
6. SR Phillips Curve: ?inflation-?unemployment (inverse).
7. Monetary policy-AD shift via interest rate changes.
8. Output gap = (Y?Y*)/Y*. Positive = inflationary, negative = recessionary.
9. “Supply increases” = rightward shift of SR?AS, not a movement up the curve.
10. Recession is defined by real GDP decline, not nominal.