Indifference Curves And Budget Lines (Copy)
7.2 Indifference Curves and Budget Lines
7.2.1 Meaning of an Indifference Curve and a Budget Line
- Indifference Curve (IC): Curve showing all combinations of two goods giving the same level of satisfaction (utility).
- Properties of ICs:
- Downward sloping (more of one good → less of the other to maintain same utility).
- Convex to the origin (diminishing marginal rate of substitution).
- Higher ICs = higher utility.
- ICs never intersect.
- Marginal Rate of Substitution (MRS):
Formula: MRS = ΔQᵧ / ΔQₓ (amount of Y given up for 1 more unit of X while keeping utility constant). - Budget Line (BL): Shows all combinations of two goods that can be purchased given income and prices.
- Formula: PₓQₓ + PᵧQᵧ = Income.
- Slope of BL = −Pₓ / Pᵧ (ratio of prices).
Example Table – IC & BL Relationship:
| Point | Good X (units) | Good Y (units) | Utility Level | Affordable? |
|---|---|---|---|---|
| A | 2 | 8 | 100 utils | Yes |
| B | 4 | 5 | 100 utils | Yes |
| C | 6 | 3 | 100 utils | No (beyond BL) |
7.2.2 Causes of a Shift in the Budget Line
- Increase in income (prices constant) → Parallel outward shift of BL.
- Decrease in income (prices constant) → Parallel inward shift of BL.
- Change in price of one good:
- Fall in price → BL pivots outwards on that axis.
- Rise in price → BL pivots inwards on that axis.
Table – Budget Line Shifts:
| Change | Effect on BL |
|---|---|
| ↑ Income | Parallel shift outward |
| ↓ Income | Parallel shift inward |
| ↓ Price of X | Pivot outward on X-axis |
| ↑ Price of X | Pivot inward on X-axis |
| ↓ Price of Y | Pivot outward on Y-axis |
| ↑ Price of Y | Pivot inward on Y-axis |
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change A2 Level Economics Full Scale Course
7.2.3 Income, Substitution and Price Effects for Normal, Inferior and Giffen Goods
Substitution Effect (SE)
- Change in consumption due to change in relative prices keeping real income constant.
- Price ↓ for X → X relatively cheaper → consume more X, less Y.
Income Effect (IE)
- Change in consumption due to change in real purchasing power from a price change.
- Price ↓ for X → real income ↑ → more of both goods (if normal).
Normal Good:
- SE → ↑ Qd for cheaper good.
- IE → ↑ Qd.
- Total effect: strong increase in Qd.
Inferior Good:
- SE → ↑ Qd for cheaper good.
- IE → ↓ Qd (but smaller).
- Total effect: Qd still rises if SE > IE.
Giffen Good:
- SE → ↑ Qd for cheaper good.
- IE (strong negative) → ↓ Qd so much it outweighs SE.
- Total effect: Qd falls when price falls (upward-sloping demand curve).
Example Table – Effects by Good Type:
| Good Type | Substitution Effect | Income Effect | Total Effect |
|---|---|---|---|
| Normal | Positive | Positive | Positive |
| Inferior | Positive | Negative | Usually Positive |
| Giffen | Positive | Strong Negative | Negative |
Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change A2 Level Economics Full Scale Course
7.2.4 Limitations of the Model of Indifference Curves
Table – Key Limitations:
| Limitation | Explanation |
|---|---|
| Assumes rational behaviour | Consumers may not always act logically. |
| Assumes clear preferences | In reality, preferences may be unclear or change. |
| Assumes perfect information | Consumers may lack knowledge of all options. |
| Ignores indivisibility of goods | Some goods cannot be divided into small units. |
| Ignores external influences | Social, cultural, behavioural factors affect choices. |