Economics: Demand, Supply, Public Goods, and Market Equilibrium (Lecture Notes)

Demand and Market Demand

• Demand is the relationship between price and the quantity a consumer is willing to buy during a given period.
• Each individual has their own demand curve; market demand is the horizontal sum of all individual demands.
• For a homogeneous good, we can aggregate demand across individuals to get the market demand curve.
• Example: coffee as a homogeneous good with a price axis on the vertical and quantity on the horizontal. At different prices, different numbers of people buy a cup of coffee.
• Formal idea:
  • Individual demand: a function q_i(p) for each person i.
  • Market demand: $Q<em>D(p) = \sum</em>{i=1}^{N} q_i(p)$.
• Illustrative price points from the lecture:
  • At price $p = 3$, many people buy a cup of coffee.
  • At price $p = 1$, even more would buy.
  • A market price of $p = 4$ yields two buyers (from the speaker’s diagram): one at each market participant’s decision point.
  • A market price of $p = 5$ would yield even fewer buyers.
• Not all goods are homogeneous; for example, two copies of a book can be heterogeneous (one signed by the author) vs. an unsigned copy.
• Homogeneous vs heterogeneous goods:
  • Homogeneous good: consumers view the good as identical (e.g., cups of coffee). One unit is interchangeable with another.
  • Non-homogeneous goods: differences in attributes (e.g., a signed copy of a book) affect willingness to pay and the shape of demand.
• Applications in the lecture:
  • When a good is a private good (rival and excludable), market demand can be summed across individuals.
  • The private good example helps explain why markets produce a market demand curve for that good.

Public vs Private Goods: Excludability and Nonexcludability

• A public good is nonexcludable: once provided, you cannot easily exclude people from using it.
• A private good is excludable: providers can prevent Non-payers from consuming.
• Examples highlighted:
  • Public good: a clock everyone can see; people can benefit without paying, which is nonexcludability.
  • Public good examples emphasized: asteroid deflection system (one unit benefits all), a public library (shared access can be nonexcludable in practice within a community).
  • Private good examples: coffee cups (one person’s consumption reduces availability for others), a book that is a private possession (two copies, one signed, one unsigned).
• How to think about public goods in the market context:
  • You add the valuations of what people are prepared to pay for the public good rather than summing the physical units.
  • For public goods, you don’t need more than one unit to satisfy everyone’s demand; what matters is the total value placed on that unit by all individuals.
• The clock example for a public good:
  • Everyone can enjoy the clock’s time regardless of who pays; the benefit is shared.
  • For a public clock, there is nonexcludability and nonrivalry in consumption.
• A key nuance raised: some goods lie on the border between private and public characteristics (partial nonexcludability), like a public library where there is some nonexcludability but membership controls exist.
• Private groups versus public goods:
  • In the week’s scope, the discussion shifts to private groups where goods are excludable and rival.

Valuation, Substitutability, and Examples

• Encyclopedia example:
  • If you have 20 volumes, you own a set.
  • If you are missing one volume, you would be willing to pay a large amount for that specific missing volume because it completes the encyclopedia-like value (transforms a set into a full encyclopedia).
• The two-copy book example:
  • If you have two copies of the same book, one signed by the author, the value of the signatures creates heterogeneity across copies.
  • The signed copy is not perfectly substitutable for the unsigned copy; valuations differ across buyers.
• Coffee as a private good example:
  • A cup of coffee is typically a homogeneous private good (excludable and rival).
  • If you leave one person’s purchase to another, the consumption by one reduces the quantity available for others, illustrating rivalry.
• Experiences and services: the ride home with a friendly neighbor or helper demonstrates excludability and the private nature of some services.

Market Equilibrium and Shifts

• Equilibrium is where demand and supply intersect: $D(p) = S(p)$, yielding an equilibrium price $P^<em>$ and quantity $Q^</em>$.
• Concept of shifts:
  • If the demand curve shifts (D1 to D2) while supply remains fixed, a new equilibrium occurs at a higher or lower price and quantity depending on the direction of the shift.
  • If the supply curve shifts (S1 to S2) while demand remains fixed, a new equilibrium occurs at a different price and quantity depending on the shift direction.
• Directional examples from the lecture:
  • Demand shift to the right (D1 → D2) due to a positive news about cigarettes (e.g., discovery that smoking enhances manhood): the new equilibrium moves to the right—higher price and higher quantity. If the supply is unchanged, the new intersection is at a higher P and higher Q (the lecture labeled this as equilibrium B).
  • Supply shift to the left (S1 → S2) due to higher production costs: the equilibrium price increases and quantity decreases. The new intersection moves to a higher price but lower quantity (the lecture labeled this as equilibrium C).
• Notation used in the lecture:
  • Demand curves labeled as D1 and D2.
  • Supply curves labeled as S1 and S2.
• Important takeaway:
  • When only one curve shifts, the new equilibrium is determined by the intersection with the fixed curve.
• Practical exam notes:
  • A quiz will test understanding of 16 concepts from Chapter 3 via a matching exercise.
  • A separate quiz will cover shifting supply and income effects on demand.

Intellectual Property and Economic Incentives

• Patents, trademarks, and copyrights are used to create exclusive rights and incentives for innovation.
• Key points:
  • Patents grant exclusive rights to the inventor for a period (the lecture notes specify twenty years).
  • This exclusivity creates temporary monopoly power intended to encourage invention and research.
• Equivalent economic insight:
  • The level and duration of protection balance innovation incentives with consumer welfare.
  • Different forms (patents, copyrights, trademarks) differ in scope and duration, but all restrict immediate competition to varying degrees.

Wages, Salary, and the Labor Market

• Wages are the price of labor; economists treat wage as payment for labor.
• Law and markets:
  • A minimum wage acts as a price floor that can influence employment, but the lecture notes suggest the minimum wage is often ineffective because the market-clearing wage is typically higher in many markets.
• Pay basis in practice:
  • Pay can be determined by the structure of courses taught, e.g., instructors may be paid per course; if no courses are taught, there is no pay in that period.
  • Academic salaries can depend on employment status (full-time vs sabbatical) and the number of courses taught.
• Illustrative personal context:
  • The lecturer describes their own pay structure (paid by the course), the number of courses they teach, and the administrative realities around housing and retirement planning.

Supply Curve and Its Implications

• The supply curve is typically upward sloping: as price rises, producers are willing to supply more of the good.
• This upward slope reflects increasing marginal costs and/or increasing opportunity costs of production.
• The lecture emphasizes the relationship between price and quantity supplied.

Study Structure and Practice Questions

• Exercises are designed around 16 core concepts split into four groups of four each.
• Students are encouraged to use the textbook and instructor’s examples to verify understanding.
• Quizzes will cover:
  • Shifts in demand and supply and the resulting equilibrium changes.
  • The effect of income changes on demand for goods such as food (e.g., rich vs poor income effects).
• Real-world relevance: understanding demand, supply, public vs private goods, and incentives helps interpret everyday price changes, policy effects, and innovation incentives.

Real-World Relevance and Takeaways

• The interplay between excludability and rivalry determines whether a good is a private or public good, shaping how markets allocate resources.
• Public goods require collective valuation; providing one unit benefits all, so social planning or collective financing often matters more than private markets for these goods.
• Intellectual property rights create incentives for innovation by temporarily restricting competition, but must be balanced against social welfare.
• Wage dynamics and minimum wage policies reflect macroeconomic policy choices that interact with labor supply, demand, and overall employment levels.
• Understanding shifts in demand and supply helps explain how various external factors (health information, costs of production, income changes) influence prices and quantities in markets.

Summary of Key Formulas and Concepts

• Market demand from individual demands:
  • $Q<em>D(p) = \sum</em>{i=1}^{N} q_i(p)$
• Public goods concept: add valuations across individuals; single unit can be enjoyed by all; no need for more than one unit.
• Social optimum for a public good (illustrative):
  • $\sum<em>i \frac{d v</em>i(x)}{d x} = MC(x)$
• Patent duration example: $\text{Patent duration} = 20\text{ years}$
• Demand and supply shifts:
  • Rightward demand shift: increases both price and quantity in the new equilibrium (D2 with S fixed).
  • Leftward supply shift: increases price and decreases quantity in the new equilibrium (S2 with D fixed).

Connections to Foundational Principles

• The material reinforces the law of demand and supply: price changes influence quantity demanded and supplied, and shifts in curves capture changes in market conditions.
• It shows how aggregation from individuals to markets works for homogeneous goods, and why heterogeneity matters for valuation and pricing.
• It ties to welfare economics through discussions of public vs private goods and the social value of goods that are nonexcludable.
• It links microeconomic theory to policy considerations (minimum wage, intellectual property, public goods) and real-world behavior (income effects on food expenditure).