Consumption & Investment: Theory, Factors & Real-World Impact

Core Concepts: Consumption and Investment

1. Consumption: The Engine of Demand

Consumption ($C$) is the spending by households on goods and services, excluding purchases of new housing. It is the largest component of Aggregate Demand (AD) in an economy.

Types of Consumption

• Autonomous Consumption ($C_a$): Spending that occurs even when income is zero (e.g., basic food, rent).
• Induced Consumption ($C_i$): Spending that rises with income (e.g., luxury goods, travel).
• Marginal Propensity to Consume (MPC): The fraction of additional income that households spend. $$MPC=\frac{\Delta C}{\Delta Y}$$
  • If MPC = 0.8, a ₹1,000 increase in income leads to ₹800 more spending.
• Average Propensity to Consume (APC): Total consumption divided by total income. $$APC=\frac{C}{Y}$$
• Marginal Propensity to Save (MPS): The fraction of additional income saved. $$MPS=1-MPC$$

Consumption Function

The relationship between consumption and income is linear: $$C=C_a+(MPC\times Y)$$ Example: In Nepal, if $C_a=₹500$ billion and MPC = 0.7, then:

• At $Y=₹2,000$ billion, $C=500+(0.7\times 2000)=₹1,900$ billion.

Factors Affecting Consumption

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A linear consumption curve showing $C=C_a+MPC\times Y$, with $C_a$ as the y-intercept and MPC as the slope. Label points for Nepal’s 2023 GDP (₹3.5 trillion) and consumption (₹2.5 trillion).

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2. Investment: The Growth Driver

Investment ($I$) is spending by businesses on capital goods (machinery, buildings, inventory) and residential construction. It is volatile and heavily influenced by expectations.

Types of Investment

Accelerator Theory

Investment depends on expected future demand: $$I=I_0+v\times (Y_t-Y_{t-1})$$

• $v$ = accelerator coefficient (how much investment changes per unit of income growth).
• Example: If Nepal’s GDP grows by 5% ($Y_t-Y_{t-1}=5\%$), and $v=2$, then investment increases by 10%.

Factors Affecting Investment

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A downward-sloping curve showing how investment falls as interest rates rise. Mark Nepal’s 2023 corporate bond rate (8%) and corresponding investment level (₹400 billion).

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In the Real World

1. Daraz’s Inventory Cycles

   • Idea Used: Accelerator Theory + Unplanned Investment
   • How? Daraz increases inventory before Dashain (induced by expected sales surge). If actual sales exceed expectations, unplanned inventory accumulation reduces reported investment (actual $I<$ planned $I$).

2. Ncell’s 5G Rollout

   • Idea Used: Interest Rates & Business Confidence
   • How? Ncell borrowed at low central bank rates (6%) to invest in 5G towers. Higher consumer demand (driven by remittances) justified the investment, increasing future profits.

3. Nepal Rastra Bank’s Loan Policies

   • Idea Used: MPC/MPS & Monetary Policy
   • How? When NRB cuts repo rates (e.g., from 8% to 7%), banks lower loan rates → households spend more (higher MPC) → businesses invest more in expansion.

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3. The Multiplier Effect: How Small Changes Have Big Impacts

The multiplier shows how an initial change in investment or government spending ripples through the economy.

$$\text{Multiplier (k)}=\frac{1}{1-MPC}=\frac{1}{MPS}$$

• Example: If MPC = 0.8, then $k=\frac{1}{0.2}=5$.
  • A ₹100 billion increase in investment → ₹500 billion rise in GDP.

Trace Through the Economy:

1. Initial Investment: ₹100 billion (e.g., NTC builds a new tower).
2. First Round: Workers spend ₹80 billion (MPC = 0.8).
3. Second Round: Those workers spend ₹64 billion, and so on.
4. Total Impact: ₹500 billion GDP increase.

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Bars showing ₹100B initial investment, then ₹80B, ₹64B, etc., summing to ₹500B. Label each bar with the round number and MPC application.

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4. Comparing Consumption and Investment

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5. Worked Example: Nepal’s Economic Growth Drivers

Scenario: Nepal’s GDP grows by 5% in 2024. How does this affect consumption and investment?

Step 1: Calculate New Consumption

• Given:
  • Initial GDP ($Y_0$) = ₹3,000 billion
  • MPC = 0.7
  • Autonomous consumption ($C_a$) = ₹500 billion
• New GDP ($Y_1$) = ₹3,150 billion (5% growth).
• New Consumption: $$C_1=500+(0.7\times 3150)=₹2,705\text{ billion}$$
  • Increase in Consumption = ₹2,705B - ₹2,600B (initial) = ₹105 billion.

Step 2: Calculate Investment via Accelerator

• Given:
  • Accelerator coefficient ($v$) = 1.5
  • Income growth ($Y_1-Y_0$) = ₹150 billion
• New Investment: $$I_1=I_0+v\times (Y_1-Y_0)=400+(1.5\times 150)=₹625\text{ billion}$$
  • Increase in Investment = ₹625B - ₹400B = ₹225 billion.

Step 3: Multiplier Effect on GDP

• Total GDP Increase: $$\Delta Y=\text{Multiplier}\times \Delta I=5\times 225=₹1,125\text{ billion}$$
  • But initial growth was only ₹150 billion → additional ₹975 billion from multiplier.

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Pie chart showing:

• Consumption (C): 75% (₹2,705B)
• Investment (I): 20% (₹625B)
• Government (G): 10% (₹315B)
• Net Exports (X-M): -5% (₹-150B)

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Exam Tip

1. Memorize Key Formulas:

   • $C=C_a+MPC\times Y$
   • $MPS=1-MPC$
   • Multiplier $k=\frac{1}{MPS}$
   • Accelerator $I=I_0+v\times (Y_t-Y_{t-1})$

2. Graphs Are Critical:

   • Always draw consumption and saving curves with:
     • $C_a$ as the y-intercept.
     • 45° line where $C=Y$ (break-even income).
   • For investment, plot interest rate vs. investment (downward slope).

3. Real-World Applications:

   • Ncell’s 5G: Link to interest rates and business confidence.
   • Daraz Sales: Use accelerator theory for inventory cycles.
   • Remittances: Explain via MPC (how ₹1,000 extra income increases spending).

4. Common Pitfalls:

   • Confusing MPC and APC: MPC is marginal (change in C/change in Y); APC is average (C/Y).
   • Ignoring Autonomous Components: Always include $C_a$ or $I_0$ in calculations.
   • Multiplier Direction: A fall in investment reduces GDP by $k\times \Delta I$.

5. Numerical Questions:

   • If given APC = 0.9 and income = ₹2,000B, calculate:
     • $C=APC\times Y=0.9\times 2000=₹1,800B$
     • $S=Y-C=₹200B$
     • $MPC=\Delta C/\Delta Y$ (if new income is ₹2,100B and new $C=₹1,890B$, then MPC = 0.9).

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Final Note: Consumption and investment are the dual engines of economic growth. While consumption is stable and income-driven, investment is volatile and forward-looking. Mastering their interactions—through multipliers, accelerators, and real-world examples—will give you an edge in exams and economic analysis. Practice with Nepal’s data (e.g., NRB reports, NEPSE trends) to solidify concepts.