Summary of Indifference Approach to Consumer Behavior
Indifference Approach to Consumer Behavior Explained
Introduction
Changes in equilibrium examine how a consumer's chosen bundle and welfare respond when external variables change: prices, income, or other constraints. This material focuses on the consequences of such changes, how to decompose effects, and how to trace resulting demand movements. It avoids detailed discussion of indifference curves, budget lines, ordinal vs cardinal utility, and basic consumer equilibrium theory (these are covered elsewhere) and instead builds on those concepts to explain how equilibrium shifts and why.
Definition: An equilibrium change is the movement from one affordable optimal consumption choice to a different one when exogenous parameters (prices, income) change.
1. Types of Changes That Alter Consumer Equilibrium
- Price changes of one or more goods
- Income changes (real or nominal)
- Changes in non-price constraints (e.g., rationing, taxes, subsidies)
- Changes in expectations or preferences (taste shifts)
Practical examples
- A rise in the price of beef due to supply disruption causes consumers to reallocate spending toward poultry or bread.
- A subsidy on public transport lowers its effective price, increasing trips taken and reducing private car rides.
2. How Equilibrium Moves: Intuition and Mechanisms
- When an exogenous variable changes, the consumer’s set of affordable bundles or relative prices change, so the optimal choice typically changes.
- Two forces often explain the net change when a single good’s price changes: the substitution effect and the income effect. These together make up the overall price effect.
Definition: The price effect is the total change in the quantity demanded of a good resulting from a change in its price. It equals the substitution effect plus the income effect.
3. Decomposing a Price Change: Substitution vs Income Effects (Conceptual)
- Substitution effect: the change in consumption due to the change in relative prices while holding real purchasing power constant. It reflects consumers substituting toward relatively cheaper goods.
- Income effect: the change in consumption due to the change in real purchasing power caused by the price change.
Key points to remember
- Substitution effect always makes the consumer move toward the relatively cheaper good.
- Income effect depends on whether the good is normal (positive income effect) or inferior (negative income effect).
4. Graphical Logic Without Repeating Basic Tools
(Background tools such as indifference maps and budget lines are assumed known. Here we discuss movement outcomes.)
- When a price of good $x$ falls, two things happen: the consumer can reach higher attainable welfare (real income rises) and relative attractiveness of $x$ increases.
- The overall change in $x$ equals the sum of substitution change and income change.
Example summary (qualitative):
- Original consumption: $x_1$
- After price falls: final consumption $x_2$
- Substitution part: $x_c - x_1$ (move holding real income constant)
- Income part: $x_2 - x_c$
5. Income Changes and the Income-Consumption Curve
- When income changes while prices are fixed, the consumer moves along an income-consumption curve that links the equilibrium bundles at each income level.
- For a normal good, consumption increases with income; for an inferior good, it may decrease.
Table: Income response patterns
| Good type | Direction of consumption when income rises | Example |
|---|---|---|
| Normal | Increase | Fresh fruit, electronics |
| Inferior | Decrease | Basic staples in some contexts (e.g., low-quality instant noodles) |
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Changes In Equilibrium
Klíčové pojmy: An equilibrium change occurs when exogenous variables (price, income, constraints) alter the consumer's optimal bundle., The total price effect equals substitution effect plus income effect., Substitution effect always moves consumption toward the relatively cheaper good., Income effect direction depends on whether a good is normal (positive) or inferior (negative)., For a normal good both substitution and income effects reinforce a price fall to increase quantity demanded., A price-consumption curve traces equilibria as one good's price changes and generates the individual demand curve., An income-consumption curve links equilibrium bundles across different income levels., Giffen goods are rare cases where income effect outweighs substitution effect, producing an upward-sloping demand segment., Taxes and subsidies can be analysed using the same substitution/income decomposition., When price rises, consumer welfare typically falls because attainable utility drops.