📖 经济周期

Economics

I. Lesson Focus

This lesson examines the definition, phases, and drivers of business cycles. Candidates must be able to identify the characteristics of expansion, peak, contraction, and trough; calculate and interpret the output gap; apply Okun’s Law to link output and unemployment; and distinguish leading, coincident, and lagging economic indicators. The focus is on using real GDP versus potential GDP to diagnose the current stage of the cycle and anticipate policy responses.

II. The Problem

A country reported GDP growth of +5.2%, –1.8%, and +4.1% over three successive years. The unemployment rate rose from 3.8% to 8.9% before falling back to 5.1%. Inventories first rose sharply and then declined rapidly while consumer confidence swung violently. CFA questions frequently require candidates to determine the current phase of the business cycle, forecast the likely policy reaction, and quantify how the output gap affects inflation and unemployment. Failure to distinguish the precise features and drivers of recession, depression, recovery, and expansion leads to incorrect answers on both multiple-choice and vignette-style questions.

III. Definition and Characteristics of Business Cycles

A business cycle is the recurrent fluctuation of actual GDP around its long-term trend (potential GDP). CFA Level I requires mastery of four primary phases: expansion, peak, contraction (recession), and trough.

• Expansion: Actual GDP growth accelerates, unemployment falls, inflationary pressure gradually builds, corporate profits rise, inventories are rebuilt, and both consumer and business confidence improve.
• Peak: Growth reaches its highest point, resources are fully utilized, inflation rises noticeably, central banks typically begin raising rates, and asset prices may exhibit bubble-like behavior.
• Contraction / Recession: Actual GDP records at least two consecutive quarters of negative growth (technical recession definition), unemployment rises, profits decline, inventories are liquidated, credit tightens, and confidence collapses.
• Trough: Economic activity bottoms, unemployment reaches its cyclical high, inflation pressure is minimal or deflation appears, and policy stimulus begins to take effect, setting the stage for the next expansion.

A complete cycle typically lasts 2–10 years. The exam emphasizes the typical behavior of economic indicators in each phase.

IV. Main Drivers of Business Cycles

Business cycles are not purely random. Key drivers include:

1. Investment and capital-stock cycles: Firms’ expectations about future demand cause volatile fixed-asset investment (acceleration principle).
2. Inventory cycles: Firms adjust stock levels to match sales; these cycles usually last 2–4 years and are a major source of short-term fluctuations.
3. External shocks: Supply shocks (oil crises), demand shocks (lockdowns), and financial shocks (2008 subprime crisis).
4. Monetary and fiscal policy: Policymakers’ reactions often amplify or dampen the cycle.
5. Confidence: Psychological factors can become self-fulfilling through consumption and investment decisions.

V. Actual GDP, Potential GDP, and the Output Gap

Potential GDP is the maximum sustainable output an economy can produce at full employment without generating inflationary pressure.

The output gap is calculated as: $$ \text{Output Gap} = \frac{\text{Actual GDP} - \text{Potential GDP}}{\text{Potential GDP}} \times 100\% $$

• Positive output gap (Actual GDP > Potential GDP): economy is overheating and inflation pressures rise.
• Negative output gap (Actual GDP < Potential GDP): slack resources exist, unemployment is elevated, and inflation pressures ease.

VI. Okun’s Law

Okun’s Law provides an empirical relationship between the output gap and unemployment. A commonly used rule of thumb for the United States is:

$$ \text{Change in Unemployment Rate} \approx -0.5 \times (\text{Actual GDP Growth} - \text{Potential GDP Growth}) $$

Equivalently, when actual GDP is 2% below potential GDP, the unemployment rate tends to be about 1% above its natural rate. This relationship allows quick assessment of labor-market pressure from output data.

VII. Economic Indicators Across the Cycle

Candidates must master the classification of indicators:

• Leading indicators: equity prices, new manufacturing orders, consumer confidence, building permits, average weekly hours.
• Coincident indicators: real GDP, industrial production, personal income, payroll employment.
• Lagging indicators: unemployment rate, unit labor costs, inventory levels, bank lending rates.

Leading indicators turn 6–9 months before GDP, coincident indicators move with GDP, and lagging indicators trail GDP by 3–6 months.

Worked Cases

Case 1: Output-Gap Calculation and Policy Implications

A country’s actual GDP in 2023 is CNY 105 trillion and estimated potential GDP is CNY 100 trillion. The natural unemployment rate is 5% while the actual rate is 7.5%.

Output gap: $$ \text{Output Gap} = \frac{105 - 100}{100} \times 100\% = +5\% $$

Interpretation: The economy is clearly overheating. According to Okun’s Law the actual unemployment rate should be below the natural rate, yet it is higher, suggesting either data inconsistency or an underestimated potential GDP. The central bank should consider rate hikes to cool demand.

Case 2: Inventory Cycle Impact on GDP

A manufacturer’s sales grew 8% in 2022 but inventories rose 15%. In 2023 sales fell 2% and the firm decides to cut inventories by 20%. Assuming other factors constant, calculate the direct drag on 2023 GDP.

A 20% inventory reduction on an opening stock of CNY 100 billion equals a CNY 20 billion decline in inventory investment, directly subtracting CNY 20 billion from GDP. If the firm represents 0.5% of national GDP, the inventory drawdown reduces national GDP growth by approximately 0.1 percentage point. This illustrates how involuntary inventory accumulation followed by liquidation drives short-term economic contraction.

Case 3: Cycle-Stage Identification and Policy Forecast

2024 data for a country: real GDP quarter-on-quarter growth of –0.8% and –1.2% (two consecutive negative quarters), unemployment rising from 4.2% to 6.8%, CPI falling from 3.1% to 0.9%, and the leading-indicator composite index down 12%. The inventory-to-sales ratio declined from 1.35 to 1.15.

Diagnosis: The economy has entered recession (technical recession confirmed by two negative quarters, sharply higher unemployment, and falling inflation). The central bank is most likely to cut rates and implement quantitative easing; fiscal policy is likely to increase infrastructure spending. The next phase is expected to be the trough, followed by recovery.

Traps

Key Formulas

• Output Gap = $\frac{\text{Actual GDP} - \text{Potential GDP}}{\text{Potential GDP}} \times 100\%$
• Okun’s Law (simplified): $\Delta U \approx -0.5 \times (\text{Actual GDP Growth} - \text{Potential GDP Growth})$
• Technical recession: two consecutive quarters of negative real GDP growth
• Natural unemployment rate = frictional + structural unemployment (cyclical unemployment = 0)
• Leading indicators change 6–9 months ahead of GDP; lagging indicators trail by 3–6 months

Practice Questions

Q1. Which of the following is most characteristic of the late expansion phase?
A. Rising unemployment and falling inflation
B. Sharp decline in business inventories
C. Actual GDP growth at its highest point and central bank beginning to raise rates
D. Consumer confidence at historic lows

Q2. If a country’s actual GDP is CNY 98 trillion and potential GDP is CNY 100 trillion, the output gap is closest to:
A. +2%
B. –2%
C. 0
D. +4%

Q3. According to Okun’s Law, if actual GDP growth is 4% below potential GDP growth, the unemployment rate is most likely higher than the natural rate by how many percentage points?
A. 1
B. 2
C. 4
D. 8

Q4. Which of the following is a leading economic indicator?
A. Unemployment rate
B. Industrial production
C. New manufacturing orders
D. Unit labor costs

Q5. The trough phase of the business cycle is most likely characterized by:
A. Rapidly rising inflation
B. Unemployment at its cyclical peak and policy stimulus beginning to take effect
C. Aggressive inventory rebuilding by firms
D. Actual GDP far above potential GDP

Q6. A country reports three consecutive quarters of real GDP growth of –0.5%, –1.1%, and +0.3%. The economy is most likely in:
A. Expansion
B. Recession
C. Transition from trough to recovery
D. Peak

Q7. A positive output gap is most likely to result in:
A. Rising unemployment
B. Increased inflationary pressure
C. Automatic reduction in fiscal deficit
D. Sharp central-bank rate cuts

Q8. Which statement about inventory cycles is correct?
A. Unintended inventory accumulation usually foreshadows faster GDP growth next period
B. Inventory liquidation usually accompanies economic recovery
C. Inventory cycles are an important source of short-term economic fluctuations
D. When inventory levels move in lockstep with sales, they have no effect on GDP

Answers

Takeaways

• The four phases occur in the order: expansion → peak → contraction (recession) → trough → recovery.
• The sign of the output gap directly signals whether the economy is overheating or operating with slack and determines the direction of inflation pressure.
• Leading indicators turn ahead of, coincident indicators move with, and lagging indicators trail GDP.
• Okun’s Law core: actual growth below potential growth raises the unemployment rate.
• Unintended inventory accumulation is often a warning of weakening demand; subsequent liquidation further depresses GDP.
• Policymakers normally ease at the trough and tighten near the peak, exerting counter-cyclical influence.