Microeconomics Chapter 4: Consumer and Producer Surplus

Consumer Surplus and the Demand Curve

• Willingness to Pay:

  • A consumer's willingness to pay for a good is defined as the maximum price at which he or she would buy that good.

  • It is determined by both the individual's personal tastes and their budget constraint.

  • Willingness to pay establishes a direct relationship with the demand curve.

• Individual Willingness to Pay Schedule:

  • In a used textbook market with five potential buyers, each buyer has a distinct willingness to pay:

  • Aleisha: $59

  • Brad: $45

  • Claudia: $35

  • Darren: $25

  • Edwina: $10

• Individual Consumer Surplus:

  • Individual consumer surplus is the net gain to an individual buyer from purchasing a good.

  • Formula: \n\text{Individual Consumer Surplus} = \text{Willingness to Pay} - \text{Price Paid}\n

• Total Consumer Surplus:

  • Total consumer surplus is the sum of the individual consumer surpluses of all buyers of a good in a market.

  • The general term "consumer surplus" is commonly used to refer to both individual and total consumer surplus.

• **Calculating Consumer Surplus at a Market Price of 30**:\n - Aleisha: Willingness to pay of 59. Individual consumer surplus = $59 - 30 = 29$.

  • Brad: Willingness to pay of $45. Individual consumer surplus =$45 - 30 = 15.\n - Claudia: Willingness to pay of 35. Individual consumer surplus = $35 - 30 = 5$.

  • Darren: Willingness to pay of $25. Since$25 < 30$, Darren does not purchase a book and receives$0 surplus.\n - Edwina: Willingness to pay of 10. Since $10 < 30$, Edwina does not purchase a book and receives $0$ surplus.

  • Total Consumer Surplus = $29 + 15 + 5 = 49$.

• Consumer Surplus Table Summary:

• General Rule for Consumer Surplus:

  • The total consumer surplus generated by purchases of a good at a given price is visually and mathematically equal to the area below the demand curve but above that price.

  • In continuous market demand curves (e.g., a tablet market with a price of $500$ and quantity of $1\text{ million}$ units), consumer surplus forms a shaded triangular area bounded by the vertical axis, the demand curve, and the horizontal line at the market price.

• Impact of Price Changes on Consumer Surplus:

  • A fall in the price of a good increases consumer surplus through two distinct channels:

  1. Gain to existing consumers: Buyers who would have purchased the good at the original higher price receive additional surplus due to paying less.

  2. Gain to new consumers: Buyers who were unwilling to buy at the original higher price are persuaded to buy at the lower price.

  • Example (Price drop from $30$ to $20$ in the used textbook market):

  • Aleisha's consumer surplus increases by $30 - 20 = 10$ (from $29$ to $39$).

  • Brad's consumer surplus increases by $30 - 20 = 10$ (from $15$ to $25$).

  • Claudia's consumer surplus increases by $30 - 20 = 10$ (from $5$ to $15$).

  • Darren enters the market as a new buyer: consumer surplus = $25 - 20 = 5$.

  • Total new consumer surplus = $39 + 25 + 15 + 5 = 84$ (an increase of $35$).

• Graphical Representation of Price Reduction (Continuous Curve):

  • When market price drops (e.g., tablet market price falling from $500$ to $200$):

  • The rectangle above the new price line up to the old price line represents the increase in consumer surplus gained by original buyers.

  • The triangle to the right represents the consumer surplus gained by new buyers entering the market between the original and new quantity.

Producer Surplus and the Supply Curve

• Cost and Willingness to Sell:

  • A potential seller's cost is the lowest price at which he or she is willing to sell a good.

  • Cost represents the seller's threshold or reservation price.

• Individual Producer Surplus:

  • Individual producer surplus is the net gain to a seller from selling a good.

  • Formula: \n\text{Individual Producer Surplus} = \text{Price Received} - \text{Seller's Cost}\n

• Total Producer Surplus:

  • Total producer surplus in a market is the sum of the individual producer surpluses of all sellers of a good in that market.

• Individual Seller Cost Schedule:

  • In a used textbook market with five potential sellers:

  • Andrew: $5

  • Betty: $15

  • Carlos: $25

  • Donna: $35

  • Engelbert: $45

• **Calculating Producer Surplus at a Market Price of 30**:\n - Andrew: Cost of 5. Individual producer surplus = $30 - 5 = 25$.

  • Betty: Cost of $15. Individual producer surplus =$30 - 15 = 15.\n - Carlos: Cost of 25. Individual producer surplus = $30 - 25 = 5$.

  • Donna: Cost of $35. Since$35 > 30$, Donna does not sell her book and receives$0 surplus.\n - Engelbert: Cost of 45. Since $45 > 30$, Engelbert does not sell his book and receives $0$ surplus.

  • Total Producer Surplus = $25 + 15 + 5 = 45$.

• General Rule for Producer Surplus:

  • The total producer surplus from sales of a good at a given price is equal to the area above the supply curve but below that price.

  • Example (Wheat market at a price of $5$ per bushel with $1\text{ million}$ bushels traded): Producer surplus is represented by the shaded region between the supply curve $S$ and the price line at $5$.

• Impact of Price Changes on Producer Surplus:

  • When the price of a good rises, producer surplus increases through two channels:

  1. Gain to original sellers: Sellers who supplied the good at the original lower price receive higher net gains on each unit.

  2. Gain to new sellers: Sellers who were unwilling to supply at the lower price are induced to supply by the higher price.

  • Example (Wheat market price rise from $5$ to $7$ per bushel):

  • Original quantity supplied = $1\text{ million}$ bushels; New quantity supplied = $1.5\text{ million}$ bushels.

  • The rectangular area of height $7 - 5 = 2$ and width $1\text{ million}$ represents the increase in producer surplus to original sellers.

  • The triangular area bounded between $1\text{ million}$ and $1.5\text{ million}$ bushels represents producer surplus gained by new sellers.

Total Surplus and Market Equilibrium

• Definition of Total Surplus:

  • Total surplus generated in a market is the total net gain to consumers and producers from trading in that market.

  • Formula: \n\text{Total Surplus} = \text{Consumer Surplus} + \text{Producer Surplus}\n

• Gains from Trade:

  • The presence of a market creates gains from trade, making both consumers and producers better off compared to self-sufficiency (no market).

  • Graphically, at market equilibrium $E$ (price of $30$, quantity of $1,000$ units):

  • Consumer surplus is the upper blue triangle above the price line $30$ and below the demand curve $D$.

  • Producer surplus is the lower red triangle below the price line $30$ and above the supply curve $S$.

  • Total surplus is the combined area of both regions.

Evaluating Market Efficiency: Alternate Allocations

• Efficiency Claim:

  • The maximum possible total surplus is achieved at the competitive market equilibrium.

  • Market equilibrium allocates consumption among potential consumers and sales among potential sellers in a manner that maximizes welfare.

  • To test market efficiency, consider three hypothetical interventions by a central planning authority:

• Intervention 1: Reallocating Consumption Among Consumers:

  • Definition: Taking a good away from a buyer who would purchase it in market equilibrium and giving it to a potential consumer who would not buy it in equilibrium.

  • Example: Taking a book from Ana (willingness to pay = $35$, point $A$) and giving it to Bob (willingness to pay = $25$, point $B$).

  • Result: Net reduction in consumer surplus and total surplus because value is transferred from a higher-valuing consumer to a lower-valuing consumer.

• Intervention 2: Reallocating Sales Among Sellers:

  • Definition: Taking sales away from sellers who would sell in market equilibrium and compelling potential sellers who would not sell in equilibrium to supply the good.

  • Example: Compelling Yvonne (cost = $35$, point $Y$) to sell instead of Xavier (cost = $25$, point $X$).

  • Result: Net loss in producer surplus and total surplus because production is shifted from a lower-cost producer to a higher-cost producer.

• Intervention 3: Changing the Quantity Traded:

  • Preventing mutually beneficial trades (Reducing quantity below equilibrium level $1,000$):

  • If transactions between buyers like Ana and sellers like Xavier are blocked, mutually beneficial gains from trade are lost, decreasing total surplus.

  • Forcing transactions beyond equilibrium (Increasing quantity above equilibrium level $1,000$):

  • Compelling transactions between buyers like Bob (willingness to pay = $25$) and sellers like Yvonne (cost = $35$) forces trades where seller cost exceeds buyer valuation ($35 > 25$), resulting in negative surplus and lowering total surplus.

• Four Core Functions of Competitive Market Equilibrium:

  1. Allocates consumption to potential buyers who value the good most (highest willingness to pay).

  2. Allocates sales to potential sellers who value the right to sell most (lowest cost).

  3. Ensures every consumer who makes a purchase values the good more than every seller who makes a sale, making all transactions mutually beneficial.

  4. Ensures every potential buyer who does not make a purchase values the good less than every potential seller who does not make a sale, preventing unbeneficial transactions.

Real-World Market Matching: The Case of eBay

• Historical Background:

  • Founded in 1995 by Pierre Omidyar, a computer programmer whose fiancée collected Pez candy dispensers and needed a platform to find potential sellers.

  • Pierre Omidyar and his wife accumulated a massive Pez dispenser collection and became billionaires through the creation of the platform.

• Economic Function:

  • Mission statement: "to help practically anyone trade practically anything on earth."

  • Solves market friction present in traditional Canadian garage sales, where distance and search costs prevent potential buyers and sellers from meeting.

  • Provides a centralized platform for trading unique, used, or specialized items globally.

  • Volume: In 2012, eBay facilitated over $175\text{ billion}$ in transaction volume.

  • Similar modern matching platforms include Kijiji.ca and Cottage Country Vacation Rentals.

Foundations of Market Efficiency and Key Caveats

• Key Features Driving Market Efficiency:

  • Property Rights: Legal rights that allow owners of valuable items, resources, or goods to dispose of them as they choose.

  • Prices as Economic Signals: Prices convey essential market information that coordinates independent individual decisions efficiently.

• Three Important Caveats to Market Efficiency:

  1. Equity vs. Efficiency:

  • A market outcome may be efficient, but it is not guaranteed to be fair or equitable.

  • Society often values equity; government interventions that reduce market efficiency to gain equity can be socially justified.

  1. Individual vs. Aggregate Gains:

  • Market equilibrium maximizes overall aggregate surplus, but it does not mean every single individual producer or consumer obtains their ideal personal outcome.

  • Price controls (such as price floors) can benefit specific individuals (e.g., certain sellers), but market equilibrium ensures Pareto efficiency (no person can be made better off without making someone else worse off).

  1. Market Failure:

  • In real-world scenarios, markets can fail to deliver efficiency, failing to maximize total surplus.

  • Primary sources of market failure:

    • Market Power: Monopoly or oligopoly power where individual firms manipulate price.

    • Externalities: Side effects of production or consumption (e.g., pollution) impacting third parties.

    • Inherent Problems of Goods: Asymmetric information (e.g., private info in used car markets) or public goods (e.g., national security, basic scientific research).

Key Terms

• Willingness to pay: The maximum price at which a buyer would purchase a good.

• Individual consumer surplus: The net gain to an individual buyer from purchasing a good, equal to willingness to pay minus price paid.

• Total consumer surplus: The sum of individual consumer surpluses of all buyers of a good in a market.

• Consumer surplus: A general term referring to individual or total consumer surplus.

• Cost: The lowest price at which a potential seller is willing to sell a good.

• Individual producer surplus: The net gain to an individual seller from selling a good, equal to price received minus cost.

• Total producer surplus: The sum of individual producer surpluses of all sellers of a good in a market.

• Producer surplus: A general term referring to individual or total producer surplus.

• Total surplus: The total net gain to society from trade in a good, equal to consumer surplus plus producer surplus.

• Property rights: The rights of owners of valuable items to store, use, or dispose of them as they choose.

• Economic signal: Any piece of information, such as price, that helps people make better economic decisions.

• Inefficient: A state where an economy or market misses opportunities to make some people better off without making others worse off.

• Market failure: A situation in which a market left to itself fails to organize production and consumption efficiently.