1. Decision-making and Demand and Supply Analysis

2. Thinking Economically: Marginal Analysis
Optimization Assumption: an assumption that suggests that the person in question is trying to maximize some objective
Marginal Benefit: the increase in the benefit that results from an action
Marginal Cost: the increase in the cost that results from an action
Total Net Benefits: the difference between all benefits and all costs

3. Marginal Way in Action Simplified
The Box Example
If the marginal benefit of an extra unity of the activity is greater than its marginal cost, increasing the activity will increase total net benefits.
If the marginal cost of an extra unit of the activity is greater than its marginal cost, increasing the activity will decrease total net benefits.
Therefore, to maximize total net benefits the level of an activity that maximizes total net benefits is where the marginal benefit equals the marginal cost of an extra unit of the activity.

4. Boxes
If an extra unit of the activity (trades) results in getting more boxes (MB) than are being given up (MC) the stack of boxes grows (TNB).
If an extra unit of the activity (trades) results in getting less boxes (MB) than are being given up (MC) the stack of boxes shrinks (TNB).
If an extra unit of the activity (trades) results in getting the same amount of boxes (MB) that are being given up (MC) the stack of boxes is at its tallest ( maximum TNB).

5. Maximizing Total Net Benefits
Total Way – select the level of the activity that maximizes the difference between total benefits and total costs
Marginal Way – set the marginal benefit of to the marginal cost of an extra unit
Economist prefer the later because many decisions are not all or nothing. Most times people are deciding to increase or decrease the amount of something that they are doing.

6. Basic Definitions for MB and MC and Maximization of TNB
MB=∆TB/ ∆Q=(TBNew-TBOld)/(Qnew-Qold)
MC=∆TC/ ∆Q=(TCNew-TCOld)/(Qnew-Qold)
TNB =TB-TC
Max TNB at that level of Q where MB=MC

7. Markets: The power of Demand and Supply
A market is simply an institution that bring buyers and sellers together to agree on price and quantity traded.
Competitive Markets
many sellers and buyers →no one buyer or seller affect the price or they are price takers
identical or homogeneous goods→price is the only decision factor
perfect information →there is only one price
free entry and exit →profits (economic) will be zero in the long-run
Non-Competitive Markets
Monopoly – one seller
Oligopoly – few sellers
Monopolistically Competitive – differentiated products

8. The Theory of Demand for Goods and Services
Households or consumers buy goods and services for a variety of reasons, but can we model it?
Economics assume that individuals are rational – they weigh the costs and benefits of their actions and then try and maximize TNB.
What are the benefits? Economists have modeled benefits as satisfaction or utility (an injection is useful but usually not pleasant – it provides utility).
What are the costs? Economist argue that the costs are opportunity costs – i.e. what does one give up to get a good or service.

9. A person’s preferences or tastes, along with other factors, determine the benefit from a good.
The price of the good, the price of similar or substitute goods, a person’s limited income, along with other factors, determine the opportunity costs of the good.
Basically, the theory of demand is getting the most satisfaction from the goods and service one buys given the prices of goods and one’s income.
While many factors affect demand, we begin by concentrating on the price of the good. Why? In competitive markets, the price of the good is the MC to the buyer.

10. The Law of Demand
Law of Demand – the price of a good and the quantity demanded are negatively (or inversely) related, ceteris paribus (Latin – all other things equal).
Rational behavior suggests that as the P↑ this means that the MC↑, ceteris paribus, an individual will ↓Q, it’s that simple.
Early theorists, however, concentrated on MB rather than MC. The believed that utility was measurable, so-called cardinal (after numbers) utility.
Law of Diminishing Marginal Utility
Jelly bean example and Econ U$A tape on the drought in California.
If people are to buy more (↑Q), since the MB↓, the price must fall (↓P)

11. The Law if Demand and the Income and Substitution Effects
More recent theorists use the concept of ordinal utility to come to a similar conclusion. A person is assumed to be able to rank bundles from most preferred to least preferred.
Reaches the Law of Demand with less restrictive assumptions than cardinal utility.
The Law if Demand and the Income and Substitution Effects
Substitution Effect: as the price of a good falls its opportunity cost relative to other similar or substitute goods falls, so consumers use more of the good and less of other goods
Income Effect: as the price of a good falls, the real purchasing power of income increases and consumers will buy more of the good (if the good is normal).
The effect of incomes on demand is not clear. For normal goods, increases in income, increase demand, and for inferior goods the opposite happens.

12. Cardinal utility, ordinal utility, and MB=MC, all arrive at Law of Demand.
We now look at the Law of Demand and the Theory of Demand using numbers/schedules, graphs/curves, and mathematical functions (don’t panic). These representations make it easier to understand the implications of theory, but they require study and practice.

13. Catherine’s Demand Schedule17

14. Figure 1 Catherine’s Demand Schedule and Demand Curve
Price of
Ice-Cream Cone
$3.00
2.50
1. A decrease
in price
...
2.00
1.50
A movement
along the curve
is caused by
changes in P only
1.00
0.50 1 2 3 4 5 6 7 8 9 10 11 12
Quantity of 2.
...
increases quantity
of cones demanded.
Ice-Cream Cones
Copyright © South-Western

15. In mathematical notation:
The Demand Function
PR - Price of related goods
Complements
Substitutes
Y - Income
NB - Number of Buyers (added when all individuals curves are summed together – see market demand)
T -Tastes
E -Expectations
G- Government: Taxes and Subsidies
In mathematical notation:
Qd=F (P , PR ,Y,NB,T,E,G), where F() is “related to”
Signing the determinants of demand. - is an inverse relationship and + is a direct relationship.
Market Demand Curve: The horizontal summation of all the individual demand curves (handout). In our Aplia experiment, the buyer values were ranked from high to low.

16. Movements Along vs Shifts of the Demand Curve
Demand Curve versus the Demand Function
The demand curve is created assuming ceteris paribus, so it maps only the relationship between P and QD.
The demand function shows all the determinants of demand. All the factors other than P, such a PR and Y, are shift factors.
Schedules
Changes in price are described by the demand schedule.
Shifts are shown as increases in QD at every price.
Graphs/Curves
A movement along the curve is a change in quantity demanded and is only caused by the change in the price of the good itself.
A shift of the curve is a change in demand is caused by any other factor other than the price of the good itself.
Qd=F (P | PR,Y,NB,T,E,G)

17. Figure 3 Shifts in the Demand Curve
Price of
Ice-Cream
Cone
Increase
in demand
Decrease
in demand
Demand
curve, D 2
Demand
curve, D 1
Demand curve, D 3
Quantity of
Ice-Cream Cones
Copyright©2003 Southwestern/Thomson Learning

18. Theory of Supply
Economists assume that businesses are rational as well. We assume their primary interest is maximizing profits.
Profits are the difference between total revenues and total costs. Revenues are analogous to benefits received by consumers.
Once again, we concentrate on price first. Why? In competitive markets, price is equal to MB (or marginal revenue) to firms. Every time the firm sells another unit, its revenue increases by the price of the good.

19. Law of Supply - price and the quantity supplied are positively related, ceteris paribus.
Rational behavior implies that firms try and maximize profits, where the MB = P and MC is dependent on how much output is produced.
As the P ↑, the MB ↑ → Q supplied ↑ to maximize profits.
Classical theorist approached the Law of Supply from the costs perspective. They posited that the MC ↑ as Q ↑.
Law of Diminishing Marginal Returns → LDMR comes from the productivity decline as more and more of a variable input is added to fixed input, eventually the extra output for each additional variable input will fall, ceteris paribus. Thus, MC ↑ of producing additional Q will eventually
Drilling for oil in Economics U$A video, Dairy Queen example, and growing the world’s food supply in a flower pot.

20. Law of Increasing Costs: as the production of a good increases, its opportunity cost increases (re: PPF and specialized resources)
Remember that the L of IC occurs because of resource specialization.
Both the LIC and LDMR predict that as Q ↑ up the productivity of inputs will fall and MC ↑.
The Law of Supply arises because prices must rise to cover the higher MC of producing additional units of output.
We can better work with the Law of Supply using schedules, graphs/curves, and mathematical equations.

21. Ben’s Supply Schedule 29

22. Figure 5 Ben’s Supply Schedule and Supply Curve
Price of
Ice-Cream
Cone
$3.00
2.50
1. An
increase
in price
...
2.00
1.50
Change in
Qs is a movement
And caused only by Price
1.00
0.50 1 2 3 4 5 6 7 8 9 10 11 12
Quantity of
Ice-Cream Cones 2.
...
increases quantity of cones supplied.
Copyright©2003 Southwestern/Thomson Learning

23. The Supply Function Qs=F(P,PI,PO,Te,E,NS,G)
PI - Input prices
PI -Prices of other outputs
Te -Technology
E -Expectations
NS -Number of sellers (occurs when adding individual supply curves together)
G - Government taxes and subsidies
Qs=F(P,PI,PO,Te,E,NS,G)
Market Supply: The horizontal summation of all the individual firms’ supply curves.

24. Movements vs. Shifts Again
Qs=F(P,PI,PO,Te,E,NS,G)
The price of the good itself causes movements along the supply curve or changes in the quantity supplied.
Anything other than the price of the good causes shifts in the supply curve or changes in supply.
Market supply comes from horizontally adding all the individual supply curves (see handout).

25. Figure 7 Shifts in the Supply Curve
Price of
Supply curve, S 3
Ice-Cream
curve,
Supply S 1
Cone
Supply
curve, S 2
Decrease
in supply
Increase
in supply
Quantity of
Ice-Cream Cones
Copyright©2003 Southwestern/Thomson Learning

26. Market Equilibrium
Market – an institution that bring buyers and sellers together to agree upon price and quantity traded.
Remember buyers key off of price in competitive markets because it is their MC and for sellers it is their MB.
Equilibrium price and quantity are those that clear the market (neither shortages or surpluses) because the Qd=Qs.
Disequilibrium prices and quantities
Shortage – Excess Demand
Surplus – Excess Supply
At the Pe and Qe , buyers and sellers behavior are coordinated.

27. Figure 8 The Equilibrium of Supply and Demand
Price of
Ice-Cream
Cone
Supply
Demand
Equilibrium
Equilibrium price
$2.00
Equilibrium
quantity 1 2 3 4 5 6 7 8 9 10 11 12 13
Quantity of Ice-Cream Cones
Copyright©2003 Southwestern/Thomson Learning

28. Figure 9 Markets Not in Equilibrium
(a) Excess Supply
Price of
Ice-Cream
Supply
Cone
Surplus
Demand
$2.50 10 4
2.00 7
Quantity of
Quantity
demanded
Quantity
supplied
Ice-Cream
Cones
Copyright©2003 Southwestern/Thomson Learning

29. Figure 9 Markets Not in Equilibrium
(b) Excess Demand
Price of
Ice-Cream
Supply
Cone
Demand
$2.00 7
1.50 10 4
Shortage
Quantity of
Quantity
supplied
Quantity
demanded
Ice-Cream
Cones
Copyright©2003 Southwestern/Thomson Learning

30. Figure 10 How an Increase in Demand Affects the Equilibrium
Price of
Ice-Cream
1. Hot weather increases
the demand for ice cream . . .
Cone D D
Supply
New equilibrium
$2.50 10
resulting
in a higher
price . . .
2.00 7
Initial
equilibrium
Quantity of 3.
. . .
and a higher
quantity sold.
Ice-Cream Cones
Copyright©2003 Southwestern/Thomson Learning

31. Figure 11 How a Decrease in Supply Affects the Equilibrium
Price of
1. An increase in the
price of sugar reduces
the supply of ice cream. . .
Ice-Cream
Cone S2 S1
Demand
New
equilibrium
$2.50 4
resulting
in a higher
price of ice
cream . . .
Initial equilibrium
2.00 7
Quantity of 3.
. . .
and a lower
quantity sold.
Ice-Cream Cones
Copyright©2003 Southwestern/Thomson Learning

32. Comparative Statics
Animal tracks help one to tell what kind of an animal and the direction the animal went.
Demand and supply shifts leave different tracks to help us identify them and whether they are increasing or decreasing.
Movement of either D or S (confirm with graphs)
D↓, S constant → P↓, Q↓
D↑, S constant → P↑, Q↑
S↓, D constant → P↑, Q↓
S↑, D constant → P↓, Q↑

33. Role of Prices Price play an important role in markets because it:
Coordinates buyers and seller behavior
Provides information about MC and MB
Rations the good between buyers
Determines resource allocation
Although the equilibrium graph is interested it is sterile, we are interested in what happens when circumstances change, i.e. demand and supply shocks (shifts).

34. Rocking and Rolling: Comparative Statics
When either the demand curve or the supply curve shift, Pe and Qe change predictably.
These is done by comparing two static equilibriums or comparative statics.
Demand Shifts/Shocks:
D ↑ → P ↑ Q ↑
D ↓ → P ↓ Q ↓
Supply Shifts/Shocks:
S ↑ → P ↓ Q ↑
S ↓ → P ↑ Q ↓
Like animals, D and S shocks leave unique tracks.

35. Using Comparative Statics to Predict or Explain Market Behavior
Predicting:
Demand can increase, remain the same, or decrease.
Supply can increase, remain the same, or decrease.
So comparative statics tells us that there are 9 different possible comparative static predictions

36. Explaining Markets with Tracks
If P↑Q↑ , what kind of animal is it? D or S? Which way is it going?
If P↓Q↓, explain.
If P↓Q↑, explain.
If P↑Q↓, explain.
Listening to market information on movements of P and Q, help explain what is the primary influence on the market, D or S.
NPR examples: Mad Cow and Tuition

37. The Invisible Hand
Adam Smith summarized the remarkable coordination that results even as people follow their own self-interest. He called in the ¨Invisible Hand¨.
As we saw in the Aplia experiment, consumer simply try to maximise their utility (TNB or gain) and producers try and maximize their profit (TNB or gain).
Market prices are
signals for resource allocation
coordinate consumer and producer behavior
incentives for buyers and sellers (MC for buyers and MB for sellers)
Ration scarce goods and services
Provide information about scarcity and value

38. Prices help markets allocate resources more efficiently
Prices help markets allocate resources more efficiently. Markets are efficient when
They produce what consumers want or most highly value, and
Produce those goods and services at least possible cost
In Aplia, we saw the total gain increased as we moved to the equilibrium prices and quantities.
We will explore the implications of this remarkable human creation as we proceed through the course.