Consumption & Investment: Functions, Trends & Determinants

TAKEAWAYS:

• Consumption depends on income, wealth, and expectations, following a linear or nonlinear pattern.
• Investment is volatile, driven by interest rates, business confidence, and technological change.
• The Keynesian consumption function shows how saving rises as income increases.
• Accelerator theory links investment to changes in output, not just current demand.
• Nepal’s consumption patterns reflect agricultural dependence and remittance inflows.
• Exam questions test graphs, numerical examples, and real-world policy implications.

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1. Consumption Function: What and Why

Definition: The consumption function shows the relationship between household consumption (C) and disposable income (Yd). It answers: "How much will people spend when their income changes?"

Key Idea: Not all income is spent—some is saved. The equation is: $$C=C_0+b{Y}_d$$

• $C_0$: Autonomous consumption (spending even if income = 0, e.g., on essentials).
• $b$: Marginal Propensity to Consume (MPC) = $\Delta C/\Delta Y_d$ (how much extra is spent per extra rupee earned).
• $Y_d$: Disposable income (income after taxes).

Why It Matters:

• Helps predict economic growth.
• Guides government policies (e.g., tax cuts to boost spending).
• Explains why poor countries save less (they spend almost everything).

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2. Components of Consumption

Consumption is divided into:

Nepal-Specific Note:

• Food dominates (60% of household spending) due to agriculture.
• Remittances (from abroad) increase consumption without boosting local production.
• Informal sector (e.g., local shops) relies heavily on cash consumption.

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3. Determinants of Consumption

Factors that shift the consumption function (change $C_0$ or $b$):

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4. Saving Function and the Relationship with Consumption

Saving Function: $$S=-S_0+s{Y}_d$$

• $S_0$: Dissaving (spending more than income, e.g., poor households).
• $s$: Marginal Propensity to Save (MPS) = $1-b$.

Key Relationship: $$Y_d=C+S$$

• If MPC = 0.8, then MPS = 0.2.
• Example: If income rises by Rs. 100, consumption rises by Rs. 80, saving by Rs. 20.

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5. Types of Consumption Functions

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6. Investment Function: What Drives Business Spending

Definition: The investment function shows how businesses spend on:

• Capital goods (machines, factories).
• Inventory (unsold goods).
• Housing (residential construction).

Key Equation: $$I=I_0+f(r,E,\text{Tech})$$

• $I_0$: Autonomous investment (e.g., replacing old machinery).
• $r$: Interest rate (lower $r$ → higher $I$).
• $E$: Business expectations (optimism → more investment).
• Tech: New technology reduces cost of production.

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7. Determinants of Investment

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8. Types of Investment

Why It Matters in Nepal:

• Infrastructure gaps (roads, energy) limit investment.
• Remittance-driven construction booms (e.g., houses in Kathmandu).
• Seasonal investment (e.g., pre-monsoon farm equipment purchases).

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9. Accelerator Theory: How Investment Follows Growth

Idea: Investment depends on changes in output, not just current demand. $$I=v\cdot \Delta Y$$

• $v$: Capital-output ratio (how much capital needed per unit of output).
• $\Delta Y$: Change in national income.

Example: If Nepal’s GDP grows by 7% this year, firms may invest 20% more next year to meet demand.

Graph:

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10. Consumption vs. Investment: Key Differences

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11. Numerical Examples (NEB-Style Problems)

Example 1: Consumption Function Calculation

Given:

• Autonomous consumption ($C_0$) = Rs. 500
• MPC = 0.75
• Income ($Y_d$) = Rs. 10,000

Find:

1. Consumption ($C$)
2. Saving ($S$)

Solution:

1. $C=C_0+b{Y}_d=500+0.75\times 10,000=500+7,500=\text{Rs. 8,000}$
2. $S=Y_d-C=10,000-8,000=\text{Rs. 2,000}$

Answer: Consumption = Rs. 8,000, Saving = Rs. 2,000.

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Example 2: MPC and MPS

Given:

• MPC = 0.6
• Income increases by Rs. 5,000

Find:

1. Change in consumption ($\Delta C$)
2. Change in saving ($\Delta S$)

Solution:

1. $\Delta C=\text{MPC}\times \Delta Y=0.6\times 5,000=\text{Rs. 3,000}$
2. $\Delta S=\Delta Y-\Delta C=5,000-3,000=\text{Rs. 2,000}$

Answer: $\Delta C=\text{Rs. 3,000}$, $\Delta S=\text{Rs. 2,000}$.

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Example 3: Investment and Interest Rates

Given:

• Investment function: $I=1,000-50r$
• Current interest rate ($r$) = 10%

Find:

1. Current investment ($I$)
2. Investment if $r$ falls to 5%

Solution:

1. $I=1,000-50\times 10=1,000-500=\text{Rs. 500}$
2. $I=1,000-50\times 5=1,000-250=\text{Rs. 750}$

Answer: Current $I=\text{Rs. 500}$, New $I=\text{Rs. 750}$.

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12. NEB Board-Style Questions (Practice)

Short Answer (5 marks)

1. "Explain the relationship between consumption and income with the help of a diagram. Why does the consumption function have a positive slope?"

Answer:

• Relationship: As income rises, consumption rises (but not as fast).
• Diagram: Draw a linear consumption function with $Y_d$ on X-axis and $C$ on Y-axis.
• Positive slope: People spend more when they earn more (MPC > 0).

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Long Answer (10 marks)

2. "Discuss the determinants of investment in Nepal. How does the accelerator principle explain investment fluctuations?"

Answer: Determinants:

1. Interest rates (lower rates → more loans → more investment).
2. Business confidence (e.g., post-earthquake reconstruction boom).
3. Technological change (e.g., shift to renewable energy).
4. Government policies (e.g., industrial incentives).
5. Expectations of profit (e.g., hydroelectric projects).

Accelerator Principle:

• Investment depends on changes in output, not just current demand.
• Example: If Nepal’s GDP grows by 8%, firms may invest 25% more next year to meet higher demand.
• Graph: Show a steep rise in investment when $\Delta Y$ increases.

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Data Interpretation (7 marks)

3. "Given the following data, calculate MPC and MPS. What happens to consumption if income rises by Rs. 2,000?"

Solution:

1. $\Delta Y=7,000-5,000=2,000$
2. $\Delta C=6,000-4,500=1,500$
3. MPC = $\Delta C/\Delta Y=1,500/2,000=0.75$
4. MPS = $1-\text{MPC}=0.25$
5. If $Y_d$ rises by Rs. 2,000, $\Delta C=0.75\times 2,000=\text{Rs. 1,500}$.

Answer: MPC = 0.75, MPS = 0.25. New consumption = Rs. 1,500 more.

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Exam Tip: How to Score Full Marks

1. Diagrams Are Mandatory

   • Always draw consumption, saving, and investment graphs for descriptive questions.
   • Label axes, slopes (MPC/MPS), and intercepts ($C_0$).

2. Use Real Nepal Examples

   • Link theory to Nepal:
     • "Like in Nepal, where remittances increase consumption without boosting local production..."
     • "The government’s industrial policy aims to increase investment in hydropower, following the accelerator principle."

3. Show Calculations Clearly

   • For numerical questions:
     • Write the formula first.
     • Substitute values step-by-step.
     • Box the final answer.

4. Answer in Bullet Points for Short Questions

   • Example:

     "Determinants of consumption in Nepal:"

     • Income (higher income → more spending on durables).
     • Remittances (increase disposable income).
     • Price of essentials (e.g., fuel, food).
     • Government subsidies (e.g., on fertilizers).

5. Avoid Vague Statements

   • ❌ "Consumption increases with income."
   • ✅ "Consumption increases with income at a rate equal to the MPC (e.g., if MPC = 0.8, a Rs. 1,000 income rise leads to Rs. 800 more spending)."

6. For Long Answers, Use a Structure

   • Introduction: Define the concept.
   • Body: Explain with determinants/examples.
   • Conclusion: Summarize and link to Nepal’s economy.

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Final Summary Table

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(Note: Actual data may vary; use for illustration.)