Microeconomics I: Theory of Consumer Behavior and Demand – Study Notes

Introduction to Microeconomics

What is Economics?

Economics is the study of how scarce resources are allocated to alternative uses. It emphasizes rational decision-making and optimization by economic agents, who choose the best feasible alternatives for themselves. Market mechanisms play a central role in resource allocation.

• Scarce resources: Limited availability of inputs for production and consumption.

• Rational decision-making: Economic agents aim to maximize their utility or profit.

What is Microeconomics?

Microeconomics focuses on the study of individual decisions made by consumers (households), producers (firms), and the markets for individual goods and services. It contrasts with macroeconomics, which studies the performance of the economy as a whole.

• Microeconomics: Individual choices and market interactions.

• Macroeconomics: Aggregate economic performance.

Theory of Consumer Behavior and Demand

Consumer Preferences & Choices

Consumer behavior is best understood by examining preferences, choices, budget constraints, and the consumer's optimum. Consumers select the best consumption bundle they can afford.

• Consumption bundle: A complete list of goods and services involved in the choice problem.

• Preference ranking: Given two bundles, X = (X1, X2) and Y = (Y1, Y2):

  • X > Y: Strict/strong preference (X is strictly preferred to Y)

  • X ~ Y: Indifference (equally preferred)

  • X ≥ Y: Weak preference (X is preferred at least as much as Y)

Assumptions about Preferences

• Completeness: Any two bundles can be compared.

• Reflexivity: Any bundle is at least as preferred as itself (X ≥ X).

• Transitivity: If X ≥ Y and Y ≥ Z, then X ≥ Z. This avoids circular preferences and ensures a best bundle exists.

Utility

Utility refers to the satisfaction or pleasure derived from consuming goods and services. It is subjective and varies across individuals, places, and times.

• Utility vs. Usefulness: Not synonymous; utility is subjective.

• Consumers seek to maximize utility by considering:

  • Satisfaction from extra units

  • Price paid

  • Satisfaction from alternatives

  • Prices of alternatives

Approaches to Measuring Utility

• Cardinalist approach: Utility is measurable in 'utils'.

• Ordinalist approach: Utility is ranked, not measured.

The Cardinal Utility Approach

Utility is measured by the amount of money a consumer is willing to pay for another unit of a commodity.

• Assumptions:

  • Rationality: Consumers maximize utility given income.

  • Cardinal measurability: Utility can be measured.

  • Constant marginal utility of money.

  • Diminishing marginal utility (DMU): Utility from successive units diminishes.

  • Utility is additive: $U = u_1(x_1) + u_2(x_2) + ... + u_n(x_n)$

Total and Marginal Utility

• Total Utility (TU): Total satisfaction from consuming a quantity of a commodity.

• Marginal Utility (MU): Additional utility from consuming one more unit.

  • Mathematically: $MU = \frac{\Delta TU}{\Delta Q}$

Law of Diminishing Marginal Utility (LDMU)

As more units of a commodity are consumed, the utility from each additional unit decreases, holding consumption of other commodities constant.

Consumer Equilibrium (Cardinal Approach)

• For one commodity: $MU_x = P_x$

• For multiple commodities: $\frac{MU_x}{P_x} = \frac{MU_y}{P_y} = ... = \frac{MU_n}{P_n}$

Example Table: Marginal Utility and Consumer Choice

Good X Quantity	TUx	MUx/Px	Good Y Quantity	TUy	MUy/Py
0	0	-	0	0	-
1	10	10	1	24	12
2	18	8	2	44	10
3	25	7	3	66	8
4	31	6	4	78	6
5	36	5	5	88	4
6	40	4	6	96	2
7	43	3	7	100	-

Critique of the Cardinal Approach

• Satisfaction cannot be measured objectively.

• Constant marginal utility of money is unrealistic.

• LDMU is accepted as an axiom without empirical verification.

• Ignores substitution and income effects.

• Considers only price effect on demand curve.

The Ordinal Utility Approach

Utility is ranked rather than measured. Preferences are represented by indifference curves, which are convex to the origin.

• Assumptions:

  • Consumers are rational.

  • Utility is ordinal.

  • Diminishing Marginal Rate of Substitution (MRS).

  • Preferences are transitive and consistent.

Indifference Set, Curve, and Map

• Indifference Set: Combinations of goods for which the consumer is indifferent.

Combinations	Quantity of Good X	Quantity of Good Y
A	10	2
B	6	4
C	3	6
D	2	8

• Indifference Curve: Graphical representation of indifference set; shows combinations yielding equal satisfaction.

• Indifference Map: A set of indifference curves; higher curves represent better bundles.

Properties of Indifference Curves

• Negative slope

• Do not intersect

• Higher curve preferred to lower

• Convex to the origin

Marginal Rate of Substitution (MRS)

• Rate at which a consumer is willing to substitute one good for another, keeping utility constant.

• Reflected by the slope of the indifference curve.

• Formula: $MRS_{x,y} = \frac{\Delta Y}{\Delta X}$

• Also: $MRS_{x,y} = \frac{MU_x}{MU_y}$

Special Kinds of Preferences

• Perfect substitutes: Indifference curves are straight lines.

• Perfect complements: Indifference curves are L-shaped.

• Neutral commodities: Indifference curves are vertical or horizontal lines.

• Satiation (bliss point): Indifference curves are concentric circles around the bliss point.

Budget Line or Price Line

The budget line represents all combinations of two goods that a consumer can purchase with a given income and prices.

• Equation: $P_x X + P_y Y \leq M$

• Graphically: Slope = $\frac{P_x}{P_y}$

Example: Budget Line Calculation

• Income = $86$

• Ice Cream: $P_x = 10$, Banana: $P_y = 6$

• Budget line: $Q_x P_x + Q_y P_y = 86$

• Slope: $\frac{P_y}{P_x} = \frac{6}{10} = 0.6$

Factors Influencing the Budget Line

• Income changes: Increase shifts the line outward; decrease shifts inward.

• Price changes: Change the slope and intercepts of the budget line.

Graphical Representation

• Budget line shifts with changes in income or prices.

• Intercepts: $M/P_x$ and $M/P_y$

*Additional info: These notes cover foundational microeconomic concepts including consumer preferences, utility theory, indifference curves, budget constraints, and equilibrium. The tables and graphs have been described and recreated for clarity. Equations are provided in LaTeX format for academic rigor.*