Consumer Behavior: Preferences, Indifference Curves, and Choice

Consumer Preferences

Market Baskets and Bundles

In microeconomics, a market basket (or bundle) refers to a specific combination of goods that a consumer might choose. These baskets are used to analyze and compare consumer preferences.

• Definition: A market basket is a collection of quantities of different goods.

• Example: Table 3.1 below shows alternative market baskets of food and clothing.

Market Basket	Units of Food	Units of Clothing
A	20	30
B	10	50
D	40	20
E	30	40
G	10	20
H	10	40

Basic Assumptions about Preferences

Consumer preferences are the basis for understanding how individuals make choices between different baskets of goods. Three key assumptions are made:

• Completeness: For any two baskets A and B, a consumer can state a preference for A over B, B over A, or be indifferent between them.

• Transitivity: If a consumer prefers A to B and B to C, then the consumer also prefers A to C.

• More is better than less: Consumers always prefer more of any good to less, assuming all goods are 'goods' (not 'bads').

Indifference Curves

Definition and Properties

An indifference curve represents all combinations of goods that provide the consumer with the same level of satisfaction or utility. The consumer is indifferent among these combinations.

• Each point on an indifference curve corresponds to a market basket with equal utility.

• Higher indifference curves represent higher utility levels.

Indifference Map

An indifference map is a collection of indifference curves, each representing a different utility level. It illustrates the consumer's entire preference structure over a range of baskets.

• Any basket on a higher indifference curve is preferred to any basket on a lower curve.

Key Features of Indifference Curves

• Completeness: Each basket lies on only one indifference curve.

• Transitivity: Indifference curves do not cross.

• More is better than less: Indifference curves have a negative slope and are not 'thick' (they do not overlap vertically).

Shape of Indifference Curves

• Downward Sloping: To maintain the same utility, an increase in one good must be offset by a decrease in the other.

• Convex to the Origin: Reflects a diminishing marginal rate of substitution (MRS); averages are preferred to extremes.

• Diminishing MRS: As a consumer substitutes one good for another, the amount of the good given up decreases as more is consumed.

Marginal Rate of Substitution (MRS)

The marginal rate of substitution (MRS) is the amount of one good a consumer is willing to give up to obtain one more unit of another good, keeping utility constant.

• Formula:

$MRS_{x,y} = -\frac{\Delta Y}{\Delta X}$

• The MRS is the (absolute value of the) slope of the indifference curve at any point.

Special Cases

• Perfect Substitutes: Two goods with a constant MRS; indifference curves are straight lines.

• Perfect Complements: Two goods with an MRS of zero or infinity; indifference curves are L-shaped.

• Bad: A good for which less is preferred to more.

Table: Comparison of Indifference Curve Types

Type	Shape of Indifference Curve	MRS
Perfect Substitutes	Straight line	Constant
Perfect Complements	L-shaped	Zero or infinite
Typical Goods	Convex to origin	Diminishing

Additional info: The above content is foundational for understanding consumer choice theory in microeconomics, including how preferences are modeled and how they relate to utility maximization.