The Partial Equilibrium Competitive Model

The Partial Equilibrium Competitive Model
Chapter 12 The Partial Equilibrium Competitive Model Nicholson and Snyder, Copyright ©2008 by Thomson South-Western. All rights reserved.

Quantity of x demanded = x(px,py,I)
Market Demand Assume that there are only two goods (x and y) An individual’s demand for x is Quantity of x demanded = x(px,py,I) If we use i to reflect each individual in the market, then the market demand curve is

Market Demand To construct the market demand curve, pX is allowed to vary while py and the income of each individual are held constant If each individual’s demand for x is downward sloping, the market demand curve will also be downward sloping

Market Demand To derive the market demand curve, we sum the
quantities demanded at every price px px px x1 Individual 1’s demand curve x2 Individual 2’s demand curve Market demand curve X* X x1* + x2* = X* x1* x2* px* x x x

Shifts in the Market Demand Curve
The market demand summarizes the ceteris paribus relationship between X and px changes in px result in movements along the curve (change in quantity demanded) changes in other determinants of the demand for X cause the demand curve to shift to a new position (change in demand)

Shifts in Market Demand
Suppose that individual 1’s demand for oranges is given by x1 = 10 – 2px + 0.1I py and individual 2’s demand is x2 = 17 – px I py The market demand curve is X = x1 + x2 = 27 – 3px + 0.1I I2 + py

To graph the demand curve, we must assume values for py, I1, and I2 If py = 4, I1 = 40, and I2 = 20, the market demand curve becomes X = 27 – 3px = 36 – 3px

If py rises to 6, the market demand curve shifts outward to X = 27 – 3px = 38 – 3px note that X and Y are substitutes If I1 fell to 30 while I2 rose to 30, the market demand would shift inward to X = 27 – 3px = 35.5 – 3px note that X is a normal good for both buyers

Generalizations Suppose that there are n goods (xi, i = 1,n) with prices pi, i = 1,n. Assume that there are m individuals in the economy The j th’s demand for the i th good will depend on all prices and on Ij xij = xij(p1,…,pn, Ij)

Generalizations The market demand function for xi is the sum of each individual’s demand for that good The market demand function depends on the prices of all goods and the incomes and preferences of all buyers

Elasticity of Market Demand
The price elasticity of market demand is measured by Market demand is characterized by whether demand is elastic (eQ,P < -1) or inelastic (0> eQ,P > -1)

Elasticity of Market Demand
The cross-price elasticity of market demand is measured by The income elasticity of market demand is measured by

Timing of the Supply Response
In the analysis of competitive pricing, the time period under consideration is important very short run no supply response (quantity supplied is fixed) short run existing firms can alter their quantity supplied, but no new firms can enter the industry long run new firms may enter an industry

Pricing in the Very Short Run
In the very short run (or the market period), there is no supply response to changing market conditions price acts only as a device to ration demand price will adjust to clear the market the supply curve is a vertical line

Pricing in the Very Short Run
D’ P2 When quantity is fixed in the very short run, price will rise from P1 to P2 when the demand rises from D to D’ Price S P1 D Quantity per period Q*

Short-Run Price Determination
The number of firms in an industry is fixed These firms are able to adjust the quantity they are producing they can do this by altering the levels of the variable inputs they employ

Perfect Competition A perfectly competitive industry is one that obeys the following assumptions: there are a large number of firms, each producing the same homogeneous product each firm attempts to maximize profits each firm is a price taker its actions have no effect on the market price information is perfect transactions are costless

Short-Run Market Supply
The quantity of output supplied to the entire market in the short run is the sum of the quantities supplied by each firm the amount supplied by each firm depends on price The short-run market supply curve will be upward-sloping because each firm’s short-run supply curve has a positive slope

Short-Run Market Supply Curve
To derive the market supply curve, we sum the quantities supplied at every price sA Firm A’s supply curve P P P sB Firm B’s supply curve Market supply curve Q1 S q1A + q1B = Q1 q1A q1B P1 quantity quantity Quantity

Short-Run Market Supply Function
The short-run market supply function shows total quantity supplied by each firm to a market Firms are assumed to face the same market price and the same prices for inputs

Short-Run Supply Elasticity
The short-run supply elasticity describes the responsiveness of quantity supplied to changes in market price Because price and quantity supplied are positively related, eS,P > 0

A Short-Run Supply Function
Suppose that there are 100 identical firms each with the following short-run supply curve qi (P,v,w) = 10P/3 (i = 1,2,…,100) This means that the market supply function is given by

A Short-Run Supply Function
In this case, computation of the elasticity of supply shows that it is unit elastic

Equilibrium Price Determination
An equilibrium price is one at which quantity demanded is equal to quantity supplied neither suppliers nor demanders have an incentive to alter their economic decisions An equilibrium price (P*) solves the equation:

The equilibrium price depends on many exogenous factors changes in any of these factors will likely result in a new equilibrium price

The interaction between market demand and market supply determines the equilibrium price Price S Q1 P1 D Total output per period

Market Reaction to a Shift in Demand
If many buyers experience an increase in their demands, the market demand curve will shift to the right D’ Price S Q2 P2 Equilibrium price and equilibrium quantity will both rise P1 D Q1 Total output per period

Market Reaction to a Shift in Demand
q2 P2 If the market price rises, firms will increase their level of output Price SMC SAC This is the short-run supply response to an increase in market price P1 q1 Output per period

Shifts in Supply and Demand Curves
Demand curves shift because incomes change prices of substitutes or complements change preferences change Supply curves shift because input prices change technology changes number of producers change

Shifts in Supply and Demand Curves
When either a supply curve or a demand curve shift, equilibrium price and quantity will change The relative magnitudes of these changes depends on the shapes of the supply and demand curves

Shifts in Supply Elastic Demand Inelastic Demand
Small increase in price, large drop in quantity Large increase in price, small drop in quantity Price S’ Price S’ S S P’ P’ P P D D Q’ Q Q per period Q’ Q Q per period Elastic Demand Inelastic Demand

Small increase in price, Large increase in price,
Shifts in Demand Small increase in price, large rise in quantity Large increase in price, small rise in quantity S Price Price S P’ P’ P P D’ D’ D D Q Q’ Q per period Q Q’ Q per period Elastic Supply Inelastic Supply

Mathematical Model of Supply and Demand
Suppose that the demand function is represented by QD = D(P,)  is a parameter that shifts the demand curve D/ = D can have any sign D/P = DP < 0

The supply relationship can be shown as QS = S(P,)  is a parameter that shifts the supply curve S/ = S can have any sign S/P = SP > 0 Equilibrium requires that QD = QS

To analyze the comparative statics of this model, we need to use the total differentials of the supply and demand functions: dQD = DPdP + Dd dQS = SPdP + Sd Maintenance of equilibrium requires that dQD = dQS

Suppose that the demand parameter () changed while  remains constant The equilibrium condition requires that DPdP + Dd = SPdP Because SP - DP > 0, P/ will have the same sign as D

We can convert our analysis to elasticities

Equilibria with Constant Elasticity Functions
Suppose the demand for automobiles is given by The supply for automobiles is

If I = $20,000 and w = $25 Equilibrium occurs where P* = 9,957 and Q* = 12,745,000

If I increases by 10 percent Equilibrium occurs where P* = 11,339 and Q* = 14,514,000

If instead w increases to $30 per hour Equilibrium occurs where P* = 10,381 and Q* = 12,125,000

Long-Run Analysis In the long run, a firm may adapt all of its inputs to fit market conditions profit-maximization for a price-taking firm implies that price is equal to long-run MC Firms can also enter and exit an industry perfect competition assumes that there are no special costs of entering or exiting an industry

Long-Run Analysis New firms will be lured into any market where economic profits are greater than zero the short-run industry supply curve will shift outward market price and profits will fall the process will continue until economic profits are zero

Long-Run Analysis Existing firms will leave any industry where economic profits are negative the short-run industry supply curve will shift inward market price will rise and losses will fall the process will continue until economic profits are zero

Long-Run Competitive Equilibrium
A perfectly competitive industry is in long-run equilibrium if there are no incentives for profit-maximizing firms to enter or to leave the industry this will occur when the number of firms is such that P = MC = AC and each firm operates at minimum AC

Long-Run Competitive Equilibrium
We will assume that all firms in an industry have identical cost curves no firm controls any special resources or technology The equilibrium long-run position requires that each firm earn zero economic profit

Long-Run Equilibrium: Constant-Cost Case
Assume that the entry of new firms in an industry has no effect on the cost of inputs no matter how many firms enter or leave an industry, a firm’s cost curves will remain unchanged This is referred to as a constant-cost industry

This is a long-run equilibrium for this industry P = MC = AC Price Price MC SMC S AC P1 Q1 q1 D Quantity per period Quantity per period A Typical Firm Total Market

Suppose that market demand rises to D’ D’ P2 Market price rises to P2 Q2 Price Price MC SMC S AC P1 D q1 Quantity per period Q1 Quantity per period A Typical Firm Total Market

In the short run, each firm increases output to q2 q2 Economic profit > 0 Price Price MC SMC S AC P2 P1 D’ D q1 Quantity per period Q1 Q2 Quantity per period A Typical Firm Total Market

In the long run, new firms will enter the industry S’ Economic profit will return to 0 Q3 Price MC Price SMC S AC P1 D’ D q1 Quantity per period Q1 Quantity per period A Typical Firm Total Market

The long-run supply curve will be a horizontal line (infinitely elastic) at p1 LS Price MC Price SMC S S’ AC P1 D’ D q1 Quantity per period Q1 Q3 Quantity per period A Typical Firm Total Market

Infinitely Elastic Long-Run Supply
Suppose that the total cost curve for a typical firm in the bicycle industry is C(q) = q3 – 20q q + 8,000 Demand for bicycles is given by QD = 2,500 – 3P

Infinitely Elastic Long-Run Supply
To find long-run equilibrium, we must find the minimum point on the typical firm’s average cost curve where AC = MC AC = q2 – 20q ,000/q MC = 3q2 – 40q + 100 this occurs where q = 20 If q = 20, AC = MC = $500 this will be the long-run equilibrium price

Shape of the Long-Run Supply Curve
The zero-profit condition is the factor that determines the shape of the long-run cost curve if average costs are constant as firms enter, long-run supply will be horizontal if average costs rise as firms enter, long-run supply will have an upward slope if average costs fall as firms enter, long-run supply will be negatively sloped

Long-Run Equilibrium: Increasing-Cost Industry
The entry of new firms may cause the average costs of all firms to rise prices of scarce inputs may rise new firms may impose “external” costs on existing firms new firms may increase the demand for tax-financed services

Suppose that we are in long-run equilibrium in this industry P = MC = AC Price MC SMC Price S AC P1 D q1 Quantity per period Q1 Quantity per period A Typical Firm (before entry) Total Market

Suppose that market demand rises to D’ D’ P2 Market price rises to P2 and firms increase output to q2 Q2 q2 MC Price SMC Price S AC P1 D q1 Quantity per period Q1 Quantity per period A Typical Firm (before entry) Total Market

Positive profits attract new firms and supply shifts out S’ q3 P3 Entry of firms causes costs for each firm to rise Q3 Price SMC’ MC’ Price S AC’ P1 D’ D Quantity per period Q1 Quantity per period A Typical Firm (after entry) Total Market Total Market

The long-run supply curve will be upward-sloping LS SMC’ Price MC’ Price S S’ AC’ p3 p1 D’ D q3 Quantity per period Q1 Q3 Quantity per period A Typical Firm (after entry) Total Market

Long-Run Equilibrium: Decreasing-Cost Industry
The entry of new firms may cause the average costs of all firms to fall new firms may attract a larger pool of trained labor entry of new firms may provide a “critical mass” of industrialization permits the development of more efficient transportation and communications networks

Long-Run Equilibrium: Decreasing-Cost Case
Suppose that we are in long-run equilibrium in this industry P = MC = AC Price MC Price SMC S AC P1 D q1 Quantity per period Q1 Quantity per period A Typical Firm (before entry) Total Market

Suppose that market demand rises to D’ D’ P2 Market price rises to P2 and firms increase output to q2 Q2 q2 Price MC SMC Price S AC P1 D q1 Quantity per period Q1 Quantity per period A Typical Firm (before entry) Total Market

Positive profits attract new firms and supply shifts out S’ P3 Entry of firms causes costs for each firm to fall Q3 q3 Price Price SMC’ MC’ S AC’ P1 D’ D q1 Quantity per period Q1 Q1 Quantity per period A Typical Firm (before entry) A Typical Firm (before entry) Total Market

The long-run industry supply curve will be downward-sloping Price Price SMC’ S MC’ S’ AC’ LS P1 P3 D D’ q1 q3 Quantity per period Q1 Q3 Quantity per period A Typical Firm (before entry) Total Market

Classification of Long-Run Supply Curves
Constant Cost entry does not affect input costs the long-run supply curve is horizontal at the long-run equilibrium price Increasing Cost entry increases inputs costs the long-run supply curve is positively sloped

Classification of Long-Run Supply Curves
Decreasing Cost entry reduces input costs the long-run supply curve is negatively sloped

Long-Run Elasticity of Supply
The long-run elasticity of supply (eLS,P) records the proportionate change in long-run industry output to a proportionate change in price eLS,P can be positive or negative the sign depends on whether the industry exhibits increasing or decreasing costs

Comparative Statics Analysis
Comparative statics analysis of long-run equilibria can be conducted using estimates of long-run elasticities of supply and demand In the long run, the number of firms in the industry will vary from one long-run equilibrium to another

Assume that we are examining a constant-cost industry Suppose that the initial long-run equilibrium industry output is Q0 and the typical firm’s output is q* (where AC is minimized) The equilibrium number of firms in the industry (n0) is Q0/q*

A shift in demand that changes the equilibrium industry output to Q1 will change the equilibrium number of firms to n1 = Q1/q* The change in the number of firms is determined by demand shift and the optimal output level for the typical firm

The effect of a change in input prices is more complicated we need to know how much minimum average cost is affected we need to know how an increase in long-run equilibrium price will affect quantity demanded

The optimal level of output for each firm may also be affected Therefore, the change in the number of firms becomes

Rising Input Costs and Industry Structure
Suppose that the total cost curve for a typical firm in the bicycle industry is C(q) = q3 – 20q q + 8,000 and then rises to C(q) = q3 – 20q q + 11,616 The optimal scale of each firm rises from 20 to 22 (where MC = AC)

Rising Input Costs and Industry Structure
At q = 22, MC = AC = $672 so the long-run equilibrium price will be $672 If demand can be represented by QD = 2,500 – 3P then QD = 484 This means that the industry will have 22 firms (484  22)

Producer Surplus in the Long Run
Short-run producer surplus represents the return to a firm’s owners in excess of what would be earned if output was zero the sum of short-run profits and fixed costs

In the long-run, all profits are zero and there are no fixed costs owners are indifferent about whether they are in a particular market they could earn identical returns on their investments elsewhere Suppliers of inputs may not be indifferent about the level of production in an industry

In the constant-cost case, input prices are assumed to be independent of the level of production inputs can earn the same amount in alternative occupations In the increasing-cost case, entry will bid up some input prices suppliers of these inputs will be made better off

Long-run producer surplus is the extra return that producers make by making transactions at the market price over and above what they would earn if nothing were produced the area above the long-run supply curve and below the market price

Ricardian Rent Assume that there are many parcels of land on which a particular crop may be grown the land ranges from very fertile land (low costs of production) to very poor, dry land (high costs of production)

Ricardian Rent At low prices only the best land is used
Higher prices lead to an increase in output through the use of higher-cost land the long-run supply curve is upward-sloping because of the increased costs of using less fertile land

Ricardian Rent The owners of low-cost firms will earn positive profits
Price Price MC AC S P* D q* Quantity per period Q* Quantity per period Low-Cost Firm Total Market

Ricardian Rent The owners of the marginal firm will earn zero profit
Price Price MC AC S P* D q* Quantity per period Q* Quantity per period Marginal Firm Total Market

Ricardian Rent Firms with higher costs (than the marginal firm) will stay out of the market would incur losses at a price of P* Profits earned by intramarginal firms can persist in the long run they reflect a return to a unique resource The sum of these long-run profits constitutes long-run producer surplus

Ricardian Rent Each point on the supply curve represents minimum average cost for some firm Price For each firm, P – AC represents profit per unit of output Total long-run profits can be computed by summing over all units of output S P* D Q* Quantity Total Market

Ricardian Rent The long-run profits for the low-cost firms may be reflected in the prices of the unique resources owned by those firms the more fertile the land is, the higher its price Thus, profits are said to be capitalized into inputs’ prices reflect the present value of all future profits

Ricardian Rent It is the scarcity of low-cost inputs that creates the possibility of Ricardian rent In industries with upward-sloping long-run supply curves, increases in output not only raise firms’ costs but also generate factor rents for inputs

Economic Efficiency and Welfare Analysis
The area between the demand and the supply curve represents the sum of consumer and producer surplus measures the total additional value obtained by market participants by being able to make market transactions This area is maximized at the competitive market equilibrium

Price S Consumer surplus is the area above price and below demand P * Producer surplus is the area below price and above supply D Quantity per period Q *

Price At output Q1, total surplus will be smaller S At outputs between Q1 and Q*, demanders would value an additional unit more than it would cost suppliers to produce P * D Quantity per period Q1 Q *

Mathematically, we wish to maximize consumer surplus + producer surplus = In long-run equilibria along the long-run supply curve, P(Q) = AC = MC

Maximizing total surplus with respect to Q yields U’(Q) = P(Q) = AC = MC maximization occurs where the marginal value of Q to the representative consumer is equal to market price the market equilibrium

Welfare Loss Computations
Use of consumer and producer surplus makes it possible to calculate welfare losses caused by restrictions on voluntary transactions in the case of linear demand and supply curves, the calculation is simple because the areas of loss are often triangular

Suppose that the demand is given by QD = 10 - P and supply is given by QS = P - 2 Market equilibrium occurs where P* = 6 and Q* = 4

Restriction of output to Q0 = 3 would create a gap between what demanders are willing to pay (PD) and what suppliers require (PS) PD = = 7 PS = = 5

The welfare loss from restricting output to 3 is the area of a triangle Price S 7 The loss = (0.5)(2)(1) = 1 6 5 D Quantity per period 3 4

The welfare loss will be shared by producers and consumers it will depend on the price elasticity of demand and the price elasticity of supply to determine who bears the larger portion of the loss the side of the market with the smallest price elasticity (in absolute value)

Price Controls and Shortages
Sometimes governments may seek to control prices at below equilibrium levels this will lead to a shortage The changes in producer and consumer surplus from this policy show its impact on welfare

Initially, the market is in long-run equilibrium at P1, Q1 SS Demand increases to D’ D’ LS P1 D Quantity per period Q1

In the short run, price rises to P2 P2 SS Firms would begin to enter the industry LS The price would end up at P3 P3 P1 D’ D Quantity per period Q1

Suppose that the government imposes a price ceiling at P1 SS LS P3 There will be a shortage equal to Q2 - Q1 Q2 P1 D’ D Quantity Q1

Some buyers will gain because they can purchase the good for a lower price Price SS LS P3 This gain in consumer surplus is the shaded rectangle P1 D’ D Quantity per period Q1 Q2

The gain to consumers is also a loss to producers who now receive a lower price Price SS LS The shaded rectangle therefore represents a pure transfer from producers to consumers P3 P1 D’ No welfare loss there D Quantity per period Q1 Q2

This shaded triangle represents the value of additional consumer surplus that would have been attained without the price control SS LS P3 P1 D’ D Quantity per period Q1 Q2

This shaded triangle represents the value of additional producer surplus that would have been attained without the price control SS LS P3 P1 D’ D Quantity Q1 Q2

This shaded area represents the total value of mutually beneficial transactions that are prevented by the government Price SS LS P3 P1 This is a measure of the pure welfare costs of this policy D’ D Quantity Q1 Q2

Disequilibrium Behavior
Assuming that observed market outcomes are generated by Q(P1) = min [QD(P1),QS(P1)], suppliers will be content with the outcome but demanders will not This could lead to a black market

Tax Incidence To discuss the effects of a per-unit tax (t), we need to make a distinction between the price paid by buyers (PD) and the price received by sellers (PS) PD - PS = t In terms of small price changes, we wish to examine dPD - dPS = dt

DPdPD = SPdPS = SP(dPD - dt)
Tax Incidence Maintenance of equilibrium in the market requires dQD = dQS or DPdPD = SPdPS Substituting, we get DPdPD = SPdPS = SP(dPD - dt)

Tax Incidence We can now solve for the effect of the tax on PD:
Similarly,

Tax Incidence Because eD  0 and eS  0, dPD /dt  0 and dPS /dt  0
If demand is perfectly inelastic (eD = 0), the per-unit tax is completely paid by demanders If demand is perfectly elastic (eD = ), the per-unit tax is completely paid by suppliers

Tax Incidence In general, the actor with the less elastic responses will experience most of the price change caused by the tax

Tax Incidence A per-unit tax creates a wedge between the price
PD PS A per-unit tax creates a wedge between the price that buyers pay (PD) and the price that sellers receive (PS) t Q** P* D Quantity per period Q*

Tax Incidence Buyers incur a welfare loss equal to the shaded area
Price S Buyers incur a welfare loss equal to the shaded area PD But some of this loss goes to the government in the form of tax revenue P* PS D Quantity per period Q** Q*

Tax Incidence Sellers also incur a welfare
Price S Sellers also incur a welfare loss equal to the shaded area PD But some of this loss goes to the government in the form of tax revenue P* PS D Quantity per period Q** Q*

Tax Incidence Therefore, this is the deadweight loss from the tax
Price S PD Therefore, this is the deadweight loss from the tax P* PS D Quantity per period Q** Q*

Deadweight Loss and Elasticity
All nonlump-sum taxes involve deadweight losses the size of the losses will depend on the elasticities of supply and demand A linear approximation to the deadweight loss accompanying a small tax, dt, is given by DW = -0.5(dt)(dQ)

From the definition of elasticity, we know that dQ = eDdPD  Q0/P0 This implies that dQ = eD [eS /(eS - eD)] dt Q0/P0 Substituting, we get

Deadweight losses are zero if either eD or eS are zero the tax does not alter the quantity of the good that is traded Deadweight losses are smaller in situations where eD or eS are small

Transactions Costs Transactions costs can also create a wedge between the price the buyer pays and the price the seller receives real estate agent fees broker fees for the sale of stocks If the transactions costs are on a per-unit basis, these costs will be shared by the buyer and seller depends on the specific elasticities involved

Gains from International Trade
Price Q* P* In the absence of international trade, the domestic equilibrium price would be P* and equilibrium quantity would be Q* S D Quantity per period

If the world price (PW) is less than the domestic price, the price will fall to PW PW Price S Quantity demanded will rise to Q1 and quantity supplied will fall to Q2 Q1 Q2 P* Imports = Q1 - Q2 imports D Quantity per period Q*

Price Consumer surplus rises S Producer surplus falls There is an unambiguous welfare gain P* PW D Quantity per period Q1 Q* Q2

Effects of a Tariff Suppose that the government
Price Suppose that the government creates a tariff that raises the price to PR PR S Quantity demanded falls to Q3 and quantity supplied rises to Q4 Q4 Q3 PW Imports are now Q3 - Q4 imports D Quantity per period Q2 Q1

Effects of a Tariff Consumer surplus falls Producer surplus rises
Price Consumer surplus falls S Producer surplus rises The government gets tariff revenue PR These two triangles represent deadweight loss PW D Quantity per period Q2 Q4 Q3 Q1

Quantitative Estimates of Deadweight Losses
Estimates of the sizes of the welfare loss triangle can be calculated Because PR = (1+t)PW, the proportional change in quantity demanded is

Quantitative Estimates of Deadweight Losses
Price The areas of these two triangles are S PR PW D Quantity per period Q2 Q4 Q3 Q1

Other Trade Restrictions
A quota that limits imports to Q3 - Q4 would have effects that are similar to those for the tariff same decline in consumer surplus same increase in producer surplus One big difference is that the quota does not give the government any tariff revenue the deadweight loss will be larger

Trade and Tariffs If the market demand curve is
QD = 200P-1.2 and the market supply curve is QS = 1.3P, the domestic long-run equilibrium will occur where P* = 9.87 and Q* = 12.8

Trade and Tariffs If the world price was PW = 9, QD would be 14.3 and QS would be 11.7 imports will be 2.6 If the government placed a tariff of 0.5 on each unit sold, the world price will be PW = 9.5 imports will fall to 1.0

Trade and Tariffs The welfare effect of the tariff can be calculated
DW1 = 0.5(0.5)( ) = 0.225 DW2 = 0.5(0.5)( ) = 0.175 Thus, total deadweight loss from the tariff is = 0.4

Important Points to Note:
Short-run equilibrium prices are determined by the intersection of what demanders are willing to pay (demand) and what firms are willing to produce (supply) both demanders and suppliers act as price takers

In the long run, the number of firms may vary in response to profit opportunities the assumption of free entry and exit implies that firms in a competitive industry will earn zero economic profits in the long run (P = AC)

The shape of the long-run supply curve depends on how entry affects input prices in the constant-cost case, input prices do not change and the long-run supply curve is horizontal if entry raises input costs, the long-run supply curve will have a positive slope

If shifts in long-run equilibrium affect input prices, the welfare of the suppliers of these inputs will be affected such changes can be measured by changes in the value of long-run producer surplus

The concepts of consumer and producer surplus provide useful ways of measuring the welfare impact of economic changes changes in consumer surplus represent changes in utility changes in producer surplus represent changes in the monetary returns that inputs receive

The competitive model can be used to study the impact of various economic policies it can be used to measure the transfers and welfare losses associated with price controls

The competitive model can also be applied to study taxation the model illustrates tax incidence and the welfare losses associated with taxation similar conclusions can be derived by using the competitive model to study transactions costs

A final, important application uses the competitive model to study international trading relationships it can help us identify those who win and those who lose with the opening of trade it can also be used to study the welfare implications of trade restrictions

The Partial Equilibrium Competitive Model

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