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Copyright © 2011 Pearson Addison-Wesley. All rights reserved. Chapter 2 Supply and Demand Talk is cheap because supply exceeds demand.

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Presentation on theme: "Copyright © 2011 Pearson Addison-Wesley. All rights reserved. Chapter 2 Supply and Demand Talk is cheap because supply exceeds demand."— Presentation transcript:

1 Copyright © 2011 Pearson Addison-Wesley. All rights reserved. Chapter 2 Supply and Demand Talk is cheap because supply exceeds demand.

2 Copyright © 2011 Pearson Addison-Wesley. All rights reserved. 2-2 Chapter 2 Outline 2.1Demand 2.2Supply 2.3Market Equilibrium 2.4Shocking the Equilibrium: Comparative Statistics 2.5Elasticities 2.6Effects of a Sales Tax 2.7Quantity Supplied Need Not Equal Quantity Demanded 2.8When to Use the Supply-and-Demand Model

3 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Demand The quantity of a good or service that consumers demand depends on price and other factors such as consumers’ incomes and the prices of related goods. The demand function describes the mathematical relationship between quantity demanded (Q d ), price (p) and other factors that influence purchases: p = per unit price of the good or service p s = per unit price of a substitute good p c = per unit price of a complementary good Y = consumers’ income

4 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Demand We often work with a linear demand function. Example: estimated demand function for pork in Canada. Q d = quantity of pork demanded (million kg per year) p = price of pork (in dollars per kg) p b = price of beef, a substitute good (in dollars per kg) p c = price of chicken, another substitute (in dollars per kg) Y = consumers’ income (in dollars per year) Graphically, we can only depict the relationship between Q d and p, so we hold the other factors constant.

5 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Demand Example: Canadian Pork Assumptions about p b, p c, and Y to simplify equation p b = $4/kg p c = $3.33/kg Y = $12.5 thousand

6 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Demand Example: Pork Changing the own- price of pork simply moves us along an existing demand curve. Changing one of the things held constant (e.g. p b, p c, and Y) shifts the entire demand curve. p b to $4.60 /kg Q = p+20∆p b = p + 20*0.6

7 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Summing Demand Functions Q 1 = D 1 (p) Q 2 = D 2 (p) Q =Q 1 +Q 2 =D 1 (p)+D 2 (p)

8 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Supply The quantity of a good or service that firms supply depends on price and other factors such as the cost of inputs that firms use to produce the good or service. The supply function describes the mathematical relationship between quantity supplied (Q s ), price (p) and other factors that influence the number of units offered for sale: p = per unit price of the good or service p h = per unit price of other production factors

9 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Supply We often work with a linear supply function. Example: estimated supply function for pork in Canada. Q s = quantity of pork supplied (million kg per year) p = price of pork (in dollars per kg) p h = price of hogs, an input (in dollars per kg) Graphically, we can only depict the relationship between Q s and p, so we hold the other factors constant.

10 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Assumption about p h to simplify equation p h = $1.50/kg 2.2 Supply Example: Canadian Pork

11 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Supply Example: Canadian Pork Changing the own- price of pork simply moves us along an existing supply curve. Changing one of the things held constant (e.g. p h ) shifts the entire supply curve. p h to $1.75 /kg Q= 88+40p-60∆p h Q =88+40p-60*.25

12 Copyright © 2011 Pearson Addison-Wesley. All rights reserved The Sum of Domestic and Foreign Supply 2.2 Summing Supply Functions

13 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Market Equilibrium The interaction between consumers’ demand curve and firms’ supply curve determines the market price and quantity of a good or service that is bought and sold. Mathematically, we find the price that equates the quantity demanded, Q d, and the quantity supplied, Q s : Given and,find p such that Q d = Q s : p = $3.30

14 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Market Equilibrium Graphically, market equilibrium occurs where the demand and supply curves intersect. At any other price, excess supply or excess demand results. Natural market forces push toward equilibrium Q and p.

15 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Shocking the Equilibrium: Comparative Statics Changes in a factor that affects demand, supply, or a new government policy alters the market price and quantity of a good or service. Changes in demand and supply factors can be analyzed graphically and/or mathematically. Graphical analysis should be familiar from your introductory microeconomics course. Mathematical analysis simply utilizes demand and supply functions to solve for a new market equilibrium. Changes in demand and supply factors can be large or small. Small changes are analyzed with Calculus.

16 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Shocking the Equilibrium: Comparative Statics with Discrete (large) Changes Graphically analyzing the effect of an increase in the price of hogs When an input gets more expensive, producers supply less pork at every price.

17 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Shocking the Equilibrium: Comparative Statics with Discrete (large) Changes Mathematically analyzing the effect of an increase in the price of hogs If p h increases by $0.25, new p h = $1.75 and

18 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Shocking the Equilibrium: Comparative Statics with Small Changes Demand and supply functions are written as general functions of the price of the good, holding all else constant. Supply is also a function of some exogenous (not in firms’ control) variable, a. Because the intersection of demand and supply determines the price, p, we can write the price as an implicit function of the supply- shifter, a: In equilibrium:

19 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Shocking the Equilibrium: Comparative Statics with Small Changes Given the equilibrium condition, we differentiate with respect to a using the chain rule to determine how equilibrium is affected by a small change in a: Rearranging: dp/da has the same sign as dS/da

20 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Solved Problem 2.1 ∆p & ∆Q when ∆p h ? Do Comparative Statics p =178+40p-60p h p=1.8 + p h dp/p h =1 Q=D(p(p h ))=286-20p(p h ) dQ/dp h =(dD/dp)(dp/p h )=-20*1=-20

21 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Elasticities The shape of demand and supply curves influence how much shifts in demand or supply affect market equilibrium. Shape is best summarized by elasticity.

22 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Elasticities Elasticity indicates how responsive one variable is to a change in another variable. The price elasticity of demand measures how sensitive the quantity demanded of a good, Q d, is to changes in the price of that good, p. If, then and elasticity can be evaluated at any point on the demand curve. Arc versus point elasticity

23 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Example: Elasticity of Demand Previous pork demand was Calculating price elasticity of demand at equilibrium (p=$3.30 and Q=220): Interpretation: negative sign consistent with downward-sloping demand a 1% increase in the price of pork leads to a 0.3% decrease in quantity of pork demanded

24 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Elasticity of Demand Elasticity of demand varies along a linear demand curve

25 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Q= Ap ε where 0>ε>-1 take natural log: ln Q = lnp + εlnp dlnQ/dp=ε/p (dQ/Q)/dp=ε/p (dQ/Q)/(dp/p )=ε 2.5 Constant Elasticity Demand Curves

26 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Factors Affecting Demand Elasticity 1.Availability of Substitutes 2.Time Horizon 3.Necessities vs. Luxuries 4.Purchase Size More InelasticMore Elastic Fewer SubstitutesMore Substitutes Short Run (less time)Long Run (more time) NecessitiesLuxuries Small Part of BudgetLarge Part of Budget

27 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Determinants of Elasticity of Demand 1.The availability of substitutes strongly influences the sensitivity of quantity demanded to changes in price. –For goods with fewer substitutes, consumers are unable to adjust quantity demanded significantly in response to a price increase making demand inelastic. –For goods with many substitutes, consumers can easily reduce quantity demanded as price rises by switching to those other products making demand elastic.

28 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Determinants of Elasticity of Demand 2.The time horizon influences the elasticity of demand for a good. –Immediately following a price increase, consumers may not be able to alter their consumption patterns, making demand inelastic. –Over time, however, consumers can adjust their behavior by finding substitutes making demand elastic.

29 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Determinants of Elasticity of Demand 3.The nature of the good to the consumer can also affect the elasticity of demand. –For goods considered as necessities, consumers are more reluctant to reduce quantity demanded when the price rises making demand inelastic. –When goods are considered luxuries, consumers will cut back on their purchases when the price rises, making demand elastic.

30 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Determinants of Elasticity of Demand 4.The size of the purchase relative to the consumer’s budget will influence the elasticity of demand. –Consumers are less concerned about price changes when purchases of a good represent a small portion of their incomes making demand inelastic. –Consumers become much more concerned (even worried) about price changes when purchases of a good account for a large portion of their incomes making demand elastic.

31 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Other Elasticities There are other common elasticities that are used to gauge responsiveness. income elasticity of demand cross-price elasticity of demand elasticity of supply

32 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Elasticity of Supply Quantity Price per Unit Elasticity of Supply Captures the Sensitivity of Quantity Supplied to Changes in Price Inelastic Supply Elastic Supply $40 80 …Causes a Small Increase in Quantity Supplied if Supply is Inelastic $50 The Same Price Increase 85 …Causes a Big Increase in Quantity Supplied if Supply is Elastic 170

33 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Change in Per-Unit Costs with Increased Production 2.Time Horizon 3.Share of Market for Inputs 4.Geographic Scope More InelasticMore Elastic Difficult to Increase Production at Constant Unit Cost Easy to Increase Production at Constant Unit Cost Raw MaterialsManufactured Goods Short RunLong Run Large Share of Market for InputsSmall Share of Market for Inputs Global SupplyLocal Supply 2.5 Factors Affecting Supply Elasticity

34 Copyright © 2011 Pearson Addison-Wesley. All rights reserved The main determinant of the elasticity of supply is how quickly per-unit costs increase with an increase in production. –If increased production requires much higher costs, then the supply curve will be inelastic. –If production can increase with constant costs then the supply curve will be elastic. Determinants of Elasticity of Supply

35 Copyright © 2011 Pearson Addison-Wesley. All rights reserved The time horizon influences the elasticity of supply for a good. –Immediately following a price increase, producers can expand output only using their current capacity making supply inelastic. –Over time, however, producers can expand their capacity making supply elastic. Determinants of Elasticity of Supply

36 Copyright © 2011 Pearson Addison-Wesley. All rights reserved The elasticity of supply for a good relates to its share of the market for the inputs used in production. –Supply is elastic when the industry can be expanded without causing a big increase in the demand for the industry’s inputs. –Supply is inelastic when industry expansion causes a significant increase in the demand for the industry’s inputs. Determinants of Elasticity of Supply

37 Copyright © 2011 Pearson Addison-Wesley. All rights reserved The geographic scope of the market determines the elasticity of supply for a good. –The wider the scope of the market of a good, the less elastic its supply. –The narrower the scope of the market of a good, the more elastic its supply. Determinants of Elasticity of Supply

38 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Supply Elasticity Constant-Elasticity Supply Curves Q= Ap η where 1>η>0 take natural log: ln Q = lnp + ηlnp (dQ/Q)/(dp/p)=η

39 Copyright © 2011 Pearson Addison-Wesley. All rights reserved What would be the effect of the Arctic National Wildlife Refuge (ANWR) on the world price of oil given that ε=-0.4, η=0.3, and the pre-ANWR world Q 1 =82 m barrels/day & p 1 =$50/barrel, ANWR production is 0.8 m barrels/day. pre-ANWR world linear Demand and Supply functions Demand: Qd = a 0 - a 1 P Supply: Qs = b 0 + b 1 P Use elasticity = (P/Q) × (ΔQ/ΔP) to compute a 1 and b = -(50/82)a = (50/82)b 1 a 1 = b 1 = Solve for a 0 and b 0 Qd = a 0 - a 1 P Qs = b 0 + b 1 P 82 = a (50) 82 = b (50) a 0 = 114.8b 0 = 57.4 Qd = – 0.656P Qs = P Solved Problem 2.3

40 Copyright © 2011 Pearson Addison-Wesley. All rights reserved post-ANWR supply function: Qs = P Qs = P New equilibrium p and Q? P = – 0.656P p 2 =$49.30 that is 1.4% decrease in p Q 2 =82.46 that is 0.56% increase in Q Solved Problem 2.3

41 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Effects of a Sales Tax Two types of sales taxes: Ad valorem tax is in percentage terms California’s state tax rate is 8.25%, so a $100 purchase generates $8.25 in tax revenue Specific (or unit) tax is in dollar terms U.S. gasoline tax is $0.18 per gallon Ad valorem taxes are much more common. The effect of a sales tax on equilibrium price and quantity depends on elasticities of demand and supply.

42 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Equilibrium Effects of a Sales Tax Consider the effect of a $1.05 per unit (specific) sales tax on the pork market that is collected from pork producers.

43 Copyright © 2011 Pearson Addison-Wesley. All rights reserved How Specific Tax Effects Depend on Elasticities If a unit tax, , is collected from pork producers, the price received by pork producers is reduced by this amount and our equilibrium condition becomes: Differentiating with respect to  : Rearranging indicates how the tax changes the price consumers pay:

44 Copyright © 2011 Pearson Addison-Wesley. All rights reserved How Specific Tax Effects Depend on Elasticities The equation can be expressed in terms of elasticities by multiplying through by p/Q: Tax incidence on consumers, the amount by which the price to consumers rises as a fraction of the amtount of the tax, is now easy to calculate given elasticities of demand and supply. Tax incidence on firms, the amount by which the price paid to firms rises, is simply 1 – dp/dτ

45 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Important Questions About Tax Effects Does it matter whether the tax is collected from producers or consumers? Tax incidence is not sensitive to who is actually taxed. A tax collected from producers shifts the supply curve back. A tax collected from consumers shifts the demand curve back. Under either scenario, a tax-sized wedge opens up between demand and supply and the incidence analysis is identical. Does it matter whether the tax is a unit tax or an ad valorem tax? If the ad valorem tax rate is chosen to match the per unit tax divided by equilibrium price, the effects are the same.

46 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Important Questions About Tax Effects Does it matter whether the tax is a unit tax or an ad valorem tax?

47 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Quantity Supplied Need Not Equal Quantity Demanded Price determines whether Q s = Q d A price ceiling legally limits the amount that can be charged for a product. Effective ceilings force the price below equilibrium price.

48 Copyright © 2011 Pearson Addison-Wesley. All rights reserved Quantity Supplied Need Not Equal Quantity Demanded Price determines whether Q s = Q d A price floor legally inflates the price of a product above some level. Effective floor forces the price above equilibrium price.

49 Copyright © 2011 Pearson Addison-Wesley. All rights reserved When to Use the Supply-and- Demand Model This model is appropriate in markets that are perfectly competitive: 1.There are a large number of buyers and sellers. 2.All firms produce identical products. 3.All market participants have full information about prices and product characteristics. 4.Transaction costs are negligible. 5.Firms can easily enter and exit the market. We will talk more about the perfectly competitive market in Chapter 8.


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