Supply and Demand Chapter 2
Definitions • Supply and Demand: the name of the most important model in all economics • Price: the amount of money that must be paid for a unit of output • Market: any mechanism by which buyers and sellers exchange goods or services • Output: the good or service and/or the amount of it sold
Definitions (continued) • Consumers: those people in a market who are wanting to exchange money for goods or services • Producers: those people in a market who are wanting to exchange goods or services for money • Equilibrium Price: the price at which no consumers wish they could have purchased more goods at that price; no producers wish that they could have sold more • Equilibrium Quantity: the amount of output exchanged at the equilibrium price
Quantity Demanded and Quantity Supplied • Quantity demanded: how much consumers are willing and able to buy at a particular price during a particular period of time • Quantity supplied: how much firms are willing and able to sell at a particular price during a particular period of time
Ceteris Paribus • As I talked about before economists use models to focus on what is most important • Models typically hold other variables constant to examine the effect of other variables. • For example in looking at the supply and demand for peanut butter we typically hold the price of jelly constant • We sometimes use the Latin phrase ceteris paribuswhich means “holding other things equal” to identify this case.
Demand and Supply • Demandis the relationship between price and quantity demanded, ceteris paribus. • Supplyis the relationship between price and quantity supplied, ceteris paribus.
Figuring out the demand Curve • There are really two different parts to it which are similar • One is the “extensive margin” that is who buys the good • The second is the “intensive margin” or how much of the good each person buys • Guell focuses on the intensive margin, but I want to start with the extensive as I think it is easier to think about
extensive Margin • Think about something like an ipad where there is really no reason to buy more than one • Suppose there are 5 people in the economy and this is what they are willing to pay:
Demand Curve So what does demand look like: • At $1200 I sell no ipads • At $1000 I sell to Lisa only • At $800 I sell 2 • At $600 I sell 3 • At $400 I sell 4 • And at $200 I sell5 Price ipads
Intensive Demand • Now suppose it is just one worker say me • I like to go to basketball games (either pro or college) • Suppose the seats are all the same, how many games would I go to? • At $200 per seat I would probably go to a game • At $50 per seat I would probably go to like 4 games a year • At $25 I would go to like 15 • At $5 I would go to like 20 • At $0 I would go to like 20 • Thus demand slopes down for me-the larger the price the fewer games I would go to • Demand in the economy picks up both the intensive and extensive margin
The Law of Demand The relationship between price and quantity demanded is a negative or inverse one. This occurs both on the extensive and intensive margin There are 3 reasons to expect it on the intensive margin
The Substitution Effect moves people toward the good that is now cheaper or away from the good that is now more expensive If the price of Mobil gas goes up I buy more Amoco
The Real Balances Effect • When a price increases it decreases your buying power causing you to buy less. • If I live in New York and am spending almost all of my money on rent, if rent doubles I have to move into cheaper place because I can’t afford my current place any more
The Law of Diminishing Marginal Utility • The amount of additional happiness that you get from an additional unit of consumption falls with each additional unit. • This is what was really going on with my basketball tickets-I like going but I get tired of it if I go to two many games • Pretty much any good we can think of has this characteristic
Put it all together and we are pretty confident that demand curves slope down p P q Q
Determinants of Demand • Taste • Income • Normal Goods • Inferior Goods • Price of Other Goods • Complement • Substitute • Population of Potential Buyers • Expected Price • Excise Taxes • Subsidies
Example: Demand for Eating Out When Income Falls p P q2 q1 Times Eating Out At a given price people eat out less
Example: Demand for ketchup when the price of beef falls p P q1 q2 Ketchup At a given price the People want more Ketchup
A Pitfall: Confusing Movement Along vs. Shifts in Demand Price changes cause movements along a demand curve. Other factors will cause shifts in demand. These are not the same The “Quantity Demanded” can change either because the price change or because the demand curve changed
Supply • Supply is more complicated and harder to think about than demand (at least for me) • In demand for an ipad a person buys an ipad and brings it home • In supply for an ipad you have to design it, buy all the components, build it, ship it, sell it in the store • The Law of Supply is the statement that there is a positive relationship between price and quantity supplied. • If I am trying to sell something, the higher is the price the more I will want to sell
Why Does the Law of Supply Make Sense? • Because of Increasing Marginal Costs firms require higher prices to produce more output. • Because many firms produce more than one good, an increase in the price of good A makes it (at the margin) more profitable so resources are diverted from good B to produce more of good A (think about the PPF)
The Supply Curve P $2.50 $2.00 $1.50 $1.00 $0.50 0 0 10 20 30 40 50 Q (in thousands) Supply
Number of Sellers goes up P $2.50 $2.00 $1.50 $1.00 $0.50 0 0 10 20 30 40 50 Q (in thousands) At a given price supply will increase
Price of an Input goes up P $2.50 $2.00 $1.50 $1.00 $0.50 0 0 10 20 30 40 50 Q (in thousands) At a given price supply will decrease
Market Equilibrium • A competitive market is in equilibrium when price has moved to a level at which quantity demand equals quantity supplied of that good. • Competitive markets have many buyers and sellers and none is large enough to individually affect the price. • Why do markets reach an equilibrium? • If prices are too high, there is excess supply (a surplus) and firms will lower prices. • If prices are too low, there is excess demand (a shortage) and firms will raise prices.
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P Equilibrium Demand 0 10 20 30 40 50 Q (in thousands) The Supply and Demand Model
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P Demand 0 10 20 30 40 50 Q (in thousands) What if Price Too High? Surplus
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P Demand 0 10 20 30 40 50 Q (in thousands) What if Price Too Low? Shortage
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply New Equilibrium P Old Equilibrium New Demand Demand Q/t 0 10 20 30 40 50 What if Price of a substitute Increases?
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P Old Equilibrium New Equilibrium New Demand Demand Q/t 0 10 20 30 40 50 What if Good gets bad Reviews?
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P New Supply Old Equilibrium New Equilibrium Demand Q/t 0 10 20 30 40 50 Technology Improves
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P New Supply Old Equilibrium New Equilibrium Demand Q/t 0 10 20 30 40 50 An Increase in cost of an Input
Why the New Equilibrium? • If there is a change in supply or demand then without a change in the price of the good, there will be a shortage or a surplus. • Suppose the cost of an input increased-firms would no longer be willing to sell at the same price • They raise prices • As a result consumers purchase less
$2.50 $2.00 $1.50 $1.00 $0.50 0 Supply P New Supply Demand Q/t 0 10 20 30 40 50 An Increase in cost of an Input As a result of the shortage, employers can raise prices to new equilibrium where shortage goes away shortage