Economics Exam Notes: Core Principles and Market Structures

1. Economic Models

Economics: The study of the allocation of scarce resources among alternative uses.
Microeconomics: The study of individuals' and firms' choices and how these choices create markets.
Production Possibilities Frontier (PPF): A graphical representation showing the various combinations of two goods that can be produced using available resources, assuming technology and resources are fixed.
- The PPF and Basic Principles:
  1. Scarce resources: Resources are limited, implying choices must be made.
  2. Scarcity involves opportunity costs: Producing more of one good means producing less of another. The opportunity cost is the value of the next best alternative forgone.
  3. Opportunity costs increase: As production of one good increases, the opportunity cost of producing an additional unit of that good generally rises, leading to a bowed-out PPF.
  4. Incentives matter: People respond to incentives, which influence their economic decisions.
  5. Inefficiency has real costs: Producing inside the PPF means resources are not fully utilized or are used inefficiently, resulting in missed potential output.
  6. Do markets work efficiently?: This is a fundamental question in economics, often addressed through models like supply and demand.
Supply and Demand Model: A fundamental economic model used to determine the equilibrium price and quantity of goods produced and consumed in a market.
Change in demand vs. Change in quantity demanded:
- Change in demand: Shifts the entire demand curve (e.g., due to changes in income, preferences, prices of related goods).
- Change in quantity demanded: Represents a movement along the demand curve, caused solely by a change in the good's own price.
Change in supply vs. Change in quantity supplied:
- Change in supply: Shifts the entire supply curve (e.g., due to changes in input prices, technology, number of sellers).
- Change in quantity supplied: Represents a movement along the supply curve, caused solely by a change in the good's own price.
Examples of Curve Shifts:
- Change in Demand: Changes in income (e.g., an increase in income shifts the demand curve for normal goods to the right).
- Change in Supply: Changes in wages (e.g., an increase in wages, an input cost, shifts the supply curve to the left).

2. Utility and Choices

Utility: A measure of satisfaction or happiness derived from consuming goods and services. People make choices to maximize their utility based on their preferences and budget constraints. Represented as a function: $U = U(X,Y)$ for two goods X and Y.
Preferences: Assumptions about how individuals rank bundles of goods:
- Complete: Individuals must be able to rank (compare) any two bundles of goods X and Y, stating a preference for one over the other or indifference between them.
- Transitive: Preferences are consistent. If an individual prefers X to Y, and Y to Z, then they must prefer X to Z.
- More is better: Individuals always prefer more of a good to less of it, assuming it's a 'good' and not a 'bad'.
Indifference Curve: A curve connecting different combinations of two goods that yield the same level of utility or satisfaction to an individual. All points on an indifference curve are equally attractive.
Marginal Rate of Substitution (MRS):
- Measures the rate at which an individual is willing to reduce consumption of one good (e.g., X) for an additional unit of another good (e.g., Y), while keeping the total utility constant.
- The MRS is the absolute value of the slope of the indifference curve at any given point.
Individual Choices and Constraints:
- A person's choices are constrained by their income and the prices of the goods they wish to consume.
- Budget Constraint: The total amount of money an individual has available to spend on goods. For two goods X and Y with prices $PX$ and $PY$ and income $I$ , the budget constraint is: $PX \cdot X + PY \cdot Y = I$
Utility Maximization: An individual maximizes utility by:
1. Spending all their income: Choosing a point on the budget constraint.
2. Choosing the mix of goods for which the MRS is equal to the price ratio: This occurs at the point of tangency between the highest attainable indifference curve and the budget constraint.
 - Max utility when: $MRS = \frac{PX}{PY}$
Important Types of Preferences: Examples of substitutes (goods that can be used in place of each other, like coffee and tea) and complements (goods that are typically consumed together, like coffee and sugar) are important for understanding consumer behavior.

3. Demand Curves

Demand Function: Describes the relationship showing the quantity of a good that consumers are willing and able to purchase at various prices, given other factors. For good X, it can be written as: $\text{Quantity of X demanded} = dX(PX, P_Y, I, \text{preferences})$
- $P_X$ = price of good X
- $P_Y$ = price of good Y (a related good)
- $I$ = income
Proportionate Changes in Prices and Income: If prices of all goods and income change by the same proportionate amount, there will be NO change in an individual's choices or quantity demanded, as the real purchasing power remains the same.
Price Changes and Effects:
- Price changes cause both a substitution effect and an income effect.
- Income Effect for a Good:
 - Normal good: If income increases and demand for the good increases (e_{Q,I} > 0).
 - Inferior good: If income increases and demand for the good decreases (e_{Q,I} < 0).
- Substitution Effect: If the price of good X ( $P_X$ ) increases, the quantity of X demanded generally decreases as consumers substitute away from the now (relatively) more expensive good towards other relatively cheaper goods.
Effect of Price Changes of Related Goods ( $P_Y$ ) on Demand for Good X:
- If an increase in $P_Y$ leads to an increase in the demand for good X, then they are substitutes (e.g., a rise in coffee prices increases demand for tea).
- If an increase in $P_Y$ leads to a decrease in the demand for good X, then they are complements (e.g., a rise in car prices decreases demand for tires).
Individual Demand Curves: Typically downward sloping, indicating an inverse relationship between price and quantity demanded.
- Changes in income or the prices of related goods shift the entire demand curve.
Market Demand Curves: Derived by horizontally summing the individual demand curves of all consumers in the market. They are also downward sloping.
Price Elasticity of Demand ( $e_{Q,P}$ ): Measures the responsiveness of the quantity demanded to a percentage change in price.
- Formula: $e_{Q,P} = \frac{\text{Percentage change in Q}}{\text{Percentage change in P}}$
- Elastic: e_{Q,P} < -1 (Quantity demanded changes more than proportionally to price change).
- Unit elastic: $e_{Q,P} = -1$ (Quantity demanded changes proportionally to price change).
- Inelastic: e{Q,P} > -1 (Quantity demanded changes less than proportionally to price change, or |e{Q,P}| < 1).
Income Elasticity ( $e_{Q,I}$ ): Measures the responsiveness of the quantity demanded to a percentage change in income.
- Formula: $e_{Q,I} = \frac{\text{Percentage change in Q}}{\text{Percentage change in I}}$
- Normal goods: e_{Q,I} > 0
- Inferior goods: e_{Q,I} < 0
- Luxury good: If e_{Q,I} > 1 (Demand increases more than proportionally with income).
- Necessity: If 0 < e_{Q,I} < 1 (Demand increases less than proportionally with income).
Cross-Price Elasticity ( $e_{Q,PY}$ ): Measures the responsiveness of the quantity demanded of good X to a percentage change in the price of good Y.
- Formula: $e{Q,PY} = \frac{\text{Percentage change in Q}X}{\text{Percentage change in P}Y}$
- Substitutes: e{Q,PY} > 0
- Complements: e{Q,PY} < 0

4. Production

Production Function: A mathematical relationship that shows the maximum amount of output ( $q$ ) that can be produced from any given set of inputs (e.g., Capital $K$ and Labor $L$ ), given the existing technology. Represented as: $q = f(K,L)$ .
Marginal Product: The additional output that can be produced by adding one more unit of a specific input, while holding all other inputs constant.
- Example (Marginal Product of Labor, $MP_L$ ): Shows the increase in output for an additional unit of labor input, holding capital constant.
Diminishing Marginal Productivity: A principle stating that as more and more of an input is used, its marginal product eventually falls, assuming all other inputs are held constant.
- Example: As more labor input is used with a fixed amount of capital, total output increases, but at a diminishing rate per additional worker.
Average Product of Labor ( $APL$ ): Total output divided by the total amount of labor input used: $APL = q/L$ .
Isoquant: A curve representing all possible combinations of two inputs (e.g., capital and labor) that a firm can use to produce a given, constant level of output.
Marginal Rate of Technical Substitution (MRTS):
- Measures the rate at which one input can be substituted for another (e.g., capital for labor) while keeping the level of output constant.
- The MRTS is the absolute value of the slope of the isoquant.
Returns to Scale: Describes how output changes in response to a proportional change in all inputs.
- Constant returns to scale: Output increases by the same proportion as the increase in all inputs (e.g., doubling inputs doubles output).
- Decreasing returns to scale: Output increases by less than the proportion of the increase in all inputs (e.g., doubling inputs less than doubles output).
- Increasing returns to scale: Output increases by more than the proportion of the increase in all inputs (e.g., doubling inputs more than doubles output).
Fixed Proportions Production: A production process where a firm cannot substitute one input for another; inputs must be used in a fixed ratio (e.g., one driver per truck).
Technological Progress: Represents an improvement in production methods that allows a firm to produce a given level of output with fewer inputs, or more output with the same inputs, shifting the production function upwards or isoquants inwards.

5. Costs

Labor Costs:
- Wage payments: Direct costs for labor.
- Wage rate: The amount a worker would earn in their next best alternative employment (opportunity cost of labor).
Capital Costs:
- Cost of capital as a sunk cost: If capital cannot be recovered or put to alternative use, its cost is sunk in the short run.
- Cost of capital is its rental rate ( $v$ ): The explicit or implicit cost of using a unit of capital for a period.
Entrepreneurial Costs:
- Owners of the firm formally earn the difference between revenue and costs.
- Entrepreneurial cost: The implicit cost of the owner's time and effort, equivalent to the salary the owner could earn at an alternative employment (opportunity cost).
Economic Profits and Cost Minimization:
- Total Costs ( $TC$ ): The sum of costs of all inputs. For labor ( $L$ ) at wage rate ( $w$ ) and capital ( $K$ ) at rental rate ( $v$ ): $TC = wL + vK$
- Profit ( $\pi$ ): The difference between total revenues and total costs.
  - $\pi = \text{Total Revenues} – \text{Total Costs}$
  - $\pi = Pq – wL – vK$ (where $P$ is price of output, $q$ is quantity of output)
  - $\pi = Pf(K,L) – wL – vK$ (substituting the production function)
Cost Minimizing Input Choice:
- To produce a given level of output at the lowest possible cost, a firm chooses a combination of inputs where the MRTS (the absolute slope of the isoquant) is equal to the ratio of the input prices.
- The slope of the isoquant is also equal to the ratio of the marginal products of the inputs: $MRTS = MPL/MPK$
- Therefore, to minimize costs, a firm operates at the point where: $MPL/MPK = w/v$
Firm's Expansion Path: A curve that connects the cost-minimizing input combinations a firm will choose to produce different levels of output.
Relationship between Output and Total Costs: This relationship heavily depends on whether the production function exhibits constant, decreasing, or increasing returns to scale.
Average Cost (AC): Total cost divided by the total quantity of output produced: $AC = \frac{TC}{q}$
Marginal Cost (MC): The additional cost incurred by producing one more unit of output: $MC = \frac{\text{Change in TC}}{\text{Change in q}}$
Short Run and the Long Run:
- Short run: A period of time during which at least one input (typically capital) is fixed, and cannot be easily varied by the firm.
- Long run: A period of time in which all inputs can be varied by the firm; all inputs are considered variable.
Fixed Costs (FC): Costs associated with inputs that are fixed in the short run (e.g., rent on a factory). These costs do not vary with the level of output.
Variable Costs (VC): Costs associated with inputs that can be varied in the short run (e.g., raw materials, labor). These costs change with the level of output.
Shifts in Cost Curves: Cost curves can shift due to:
- Changes in input prices: An increase in wage rates ( $w$ ) or capital rental rates ( $v$ ) will shift cost curves upwards.
- Technological innovation: Improvements in technology can reduce total production costs for any given output level, shifting cost curves downwards.
- Economies of scope: Occur when producing two or more products jointly is less costly than producing them separately.

6. Profit Maximization and Supply

Economic Profits: The difference between total revenue ( $TR$ ) and total cost ( $TC$ ), where total cost includes both explicit and implicit costs. $\pi(q) = TR(q) – TC(q)$ .
Profit Maximization Rule: A firm chooses the level of output ( $q$ ) that generates the largest profit. This occurs where Marginal Revenue (MR) equals Marginal Cost (MC): $MR = MC$ .
Marginal Revenue (MR): The additional revenue generated from selling one more unit of output.
Price Taker: A firm that can increase its output without affecting the market price of the good. In a perfectly competitive market, individual firms are price takers.
- For a price-taking firm, its marginal revenue is equal to the market price: $MR = P$ .
Price Elasticity of Demand for a Single Firm:
- If demand is elastic (e_{Q,P} < -1), then MR > 0 (selling more increases total revenue).
- If demand is inelastic (e_{Q,P} > -1), then MR < 0 (selling more decreases total revenue).
- If demand is unit elastic ( $e_{Q,P} = -1$ ), then $MR = 0$ (selling more does not change total revenue).
- The relationship between MR, P, and elasticity is: $MR = P \left(1 + \frac{1}{e_{Q,P}}\right)$
Firm's Output Decision: A firm will continue to sell output as long as its marginal cost is less than or equal to its marginal revenue ( $MC \le MR$ ).
- The marginal revenue curve will generally lie below the demand curve (which is also the average revenue curve for the firm, except for a price taker where $P = AR = MR$ ).
Profit Calculation:
- $\pi = \text{Total Revenue} – \text{Total Cost}$ (where $TC$ can be Short-Run Total Cost, $STC$ )
- $\pi = P^q^ - STC(q^*)$
- $\pi = q^[P^ - STC(q^)/q^]$
- $\pi = q^[P^ - SAC(q^*)]$ (where $SAC$ is Short-Run Average Cost)
- Profit Condition:
 - If P^* > SAC(q^*), then profit is positive (\pi > 0).
 - If $P^* = SAC(q^*)$ , then profit is zero ( $\pi = 0$ ), also known as normal profit.
 - If P^* < SAC(q^*), then profit is negative (\pi < 0), the firm incurs economic losses.
Shut Down Condition (in the Short Run):
- A firm compares its losses from continuing to produce (q > 0) versus shutting down ( $q = 0$ ).
- If the firm shuts down, it only loses its fixed costs ( $-FC$ ).
- The firm stays open and produces (q > 0) if its total revenue ( $Pq$ ) sufficiently covers its short-run variable costs ( $SVC$ ).
- Specifically, the firm stays open if its revenue exceeds its short-run variable costs: $Pq \ge SVC$
- This is equivalent to saying the price must be greater than or equal to its short-run average variable costs: $P \ge SVC/q$ or $P \ge SAVC$ . If P < SAVC, the firm should shut down immediately to minimize losses, as it can't even cover its variable costs of production.

7. Perfect Competition in a Single Market

Characteristics of a Perfectly Competitive Market:
- Prices are determined by the interaction of a large number of buyers and sellers.
- All buyers and sellers are price takers (no single participant can influence the market price).
- Homogeneous products (goods are identical).
- Free entry and exit for firms (no significant barriers).
- Perfect information for all participants.
Causes and Effects of Entry and Exit of Firms: Entry and exit are crucial for the long-run adjustment of perfectly competitive markets.
- Supply Response: The change in quantity supplied due to a change in demand conditions.
Time Frames in Perfect Competition:
1. Very Short Run (Market Period):
 - The quantity supplied is fixed and cannot be changed immediately.
 - For a change in demand, only the price changes; quantity supplied remains constant.
2. Short Run:
 - Existing firms can respond to changes in demand conditions by adjusting their variable inputs (e.g., labor).
 - No new firms can enter the market, and existing firms cannot exit.
 - Firms can increase or decrease supply based on market price.
 - Market quantity supplied ( $QS$ ) is the sum of all individual firms' supply curves ( $qs$ ).
 - Firms maximize profits by producing where $P = SMC$ (Short-Run Marginal Cost).
 - Shifts in supply can occur from changes in input prices or technology.
 - Changes in price and quantity depend on the price elasticity of both supply and demand.
3. Long Run:
 - Existing firms can vary all inputs (no fixed inputs).
 - New firms can freely enter or existing firms can exit the industry (assuming no extra costs for entry/exit).
 - Each firm maximizes profits by producing where $P = MC$ (Long-Run Marginal Cost).
 - Response to Short-Run Profits/Losses:
 - If there are short-run economic profits, new firms will be attracted to enter the industry. This increases market supply, which causes the market price to fall and lowers profits for all firms.
 - If there are short-run economic losses, existing firms will exit the industry. This decreases market supply, which causes the market price to rise and eliminates the economic losses for the remaining firms.
Long Run Equilibrium (Perfect Competition):
- $P = MC$ : Firms are maximizing profits.
- $P = AC$ : Economic profits are zero, due to the free entry and exit of firms. This means firms earn only a normal rate of return on capital.
- $P = \text{min AC} = MC$ : Each firm produces at the minimum point of its long-run average cost curve, indicating productive efficiency. The MC curve intersects the AC curve at its minimum point.
Long-Run Supply Curve (LS):
- The shape of the LS curve depends on how average costs change as the industry expands or contracts due to entry/exit.
- Perfectly elastic (horizontal): If the industry has constant average costs (constant-cost industry) when new firms enter. This means input prices do not change as industry output expands.
- Positively sloped: If the industry has increasing average costs (increasing-cost industry) when new firms enter. This happens if input prices rise as the industry expands.
- Negatively sloped: If the industry has decreasing average costs (decreasing-cost industry) when new firms enter. This can occur due to network externalities or other external economies of scale.
Network Externalities: Additional users joining a network can cause costs (e.g., information, communication) to decline or the value of the network to increase for all users. Examples include telecommunications, computer software, and the Internet.
Long-Run Supply Elasticity: Measures the responsiveness of quantity supplied to price changes in the long run. Formula: $\text{Long-run supply elasticity} = \frac{\text{Percentage change in quantity supplied}}{\text{Percentage change in price}}$

8. General Equilibrium and Welfare

Partial Equilibrium: An economic model that analyzes a single market in isolation, assuming that events in other markets do not significantly affect it, or that their effects are negligible.
General Equilibrium: An economic model that analyzes the interactions and interdependencies among all markets in an entire economic system, simultaneously determining equilibrium prices and quantities for all goods and services.
Marginal Rate of Transformation (MRT): The slope of the Production Possibilities Frontier (PPF). It measures the rate at which an economy can transform one good into another by shifting resources between their production.
Economically Efficient Point: An allocation of resources is economically efficient when the slope of the PPF equals the slope of the indifference curve, which also equals the slope of the budget constraint. This implies that the MRT (production efficiency) equals the MRS (consumption efficiency) and the price ratio (market efficiency): $\text{Slope of PPF} = \text{Slope of Indifference Curve} = \text{Slope of Budget Constraint}$ , or $MRT = MRS = PX/PY$ .
First Welfare Theorem: States that a perfectly competitive price system, under certain conditions, will lead to an economically efficient allocation of resources (a Pareto efficient outcome).
Why Markets Fail to Achieve Efficiency (Market Failures):
- Imperfect Competition: Monopoly, oligopoly, or monopolistic competition where firms have market power and can set prices above marginal cost, leading to underproduction.
- Externalities: Costs or benefits imposed on third parties not directly involved in the production or consumption of a good (e.g., pollution is a negative externality, vaccination is a positive externality).
- Public Goods: Goods that are non-rival (one person's consumption does not diminish another's) and non-excludable (difficult to prevent people from consuming even if they don't pay), leading to free-rider problems and under-provision by private markets.
- Imperfect Information: Situations where buyers or sellers (or both) lack full information about the good or service, leading to suboptimal decisions.
Edgeworth Box: A graphical tool used to depict the distribution of two goods between two individuals or the allocation of two inputs between two production processes. It demonstrates how voluntary exchange can lead to efficient allocations of goods X and Y.
Pareto Efficient: An allocation of resources where it is impossible to make any one individual better off without making at least one other individual worse off. No further mutually beneficial trading opportunities exist.
Contract Curve: In an Edgeworth Box, this is the set of all Pareto efficient points. It is the locus of points where the indifference curves of the two individuals are tangential to each other (i.e., their MRS are equal).
Equitable Distribution of Resources: While markets can achieve efficiency, this does not guarantee equity. An efficient allocation may not be equitable based on initial endowments. For example, from an initial endowment point E, it may not be possible to reach point G (which might be considered a more equitable allocation of output) through voluntary exchange alone.
- Diagram Insights: The diagram (with indifference curves $U{S1}, U{S2}, U{S3}$ for individual S and $U{J1}, U{J2}, U{J3}$ for individual J) illustrates the concept of efficiency (tangencies) within an Edgeworth box, where point E is an initial endowment and point G might represent a desired but unreachable equitable outcome through trade from E.

9. Capital and Time

Individual Savings: Individuals choose to save for two main purposes:
1. Consumption goods: To finance future consumption.
2. Investment goods: To acquire assets that can generate future income or consumption.
Two-Period Model: A simplified model of intertemporal choice where consumption ( $C$ ) and income ( $Y$ ) are considered across two time periods:
- $C_0$ = Consumption this year (present)
- $C_1$ = Consumption next year (future)
Intertemporal Budget Constraint: Shows the combinations of present and future consumption that an individual can achieve with a given income ( $Y$ ) and real interest rate ( $r$ ). It is a fundamental constraint on savings decisions:
- $C0 + \frac{C1}{1+r} = Y$
- This equation means that present consumption plus the present value of future consumption must equal present income.
Savings Decisions: These decisions are based on an individual's consumption choices over time and the prevailing real interest rate.
Optimal Choices of $C0$ and $C1$ : Occur when the individual's Marginal Rate of Substitution (MRS) between present and future consumption equals the market's rate of trade-off, which is $(1+r)$ .
- $MRS = 1 + r$
Effect of a Change in Real Interest Rate ( $r$ ) on Savings (Uncertain):
- Substitution Effect: An increase in $r$ raises the cost of current consumption ( $C0$ ) relative to future consumption ( $C1$ ). This encourages individuals to substitute away from present consumption, leading to a decrease in $C_0$ and thus an increase in savings.
- Income Effect: An increase in $r$ shifts the budget constraint. If an individual is a net saver, a higher $r$ increases their future purchasing power, making them (effectively) richer. This 'richer' effect might lead them to consume more in both periods, potentially increasing $C_0$ and thereby causing savings to fall.
- The net effect on savings is uncertain as the substitution and income effects work in opposite directions.
Implicit Cost of Capital (Rental Rate, $V$ ): This represents the opportunity cost of owning and using capital. It incorporates depreciation, the real interest rate, and taxes.
- $V = (d + r) \cdot P \cdot (1 + t)$
- $d$ = depreciation rate (the rate at which capital loses value)
- $r$ = real interest rate (the opportunity cost of funds invested in capital)
- $P$ = price of the capital good
- $t$ = taxes (specific to capital ownership/use)
Diagram Interpretation (Intertemporal Choice):
- The diagram shows an intertemporal budget constraint between $C0$ (This year) and $C1$ (Next year).
- The slope of the budget line is $-(1+r)$ .
- The maximum consumption next year (if all income is saved) is $(1+r)Y$ . The maximum consumption this year (if no income is saved) is $Y$ .
- Indifference curves ( $U1, U2, U3$ ) show combinations of $C0$ and $C_1$ that provide equal utility.
- Optimal C0^ and $C1^$ occur at the tangency point where the slope of the indifference curve (MRS) equals the slope of the budget constraint ( $(1+r)$ ).

10. Monopoly

Monopoly vs. Perfect Competition: In perfect competition, firms are price takers ( $P=MC$ ). In a monopoly, a single firm is the sole seller in a market, giving it significant market power.
Main Reason Monopolies Exist: Barriers to Entry: Factors that prevent new firms from entering a market, allowing the monopolist to maintain its market dominance and earn long-run economic profits.
- Technical Barriers to Entry:
  - Diminishing average cost over a broad range of output: Natural monopoly, where economies of scale are so extensive that a single firm can supply the entire market output at a lower average cost than multiple firms (e.g., utilities).
  - Special knowledge of a low-cost method of production: Proprietary technology or unique production expertise.
  - Ownership of a key resource: Exclusive control over a crucial input necessary for production (e.g., De Beers and diamonds).
  - Possession of unique managerial talent: Rare and indispensable entrepreneurial skills.
- Legal Barriers to Entry:
  - Patents and copyrights: Government-granted exclusive rights to produce and sell an invention or creative work for a specified period.
  - Exclusive franchise or license: Government grants a single firm the exclusive right to operate in a particular market (e.g., postal services, cable TV in some areas).
Monopoly Profit Maximization:
- A monopoly maximizes profits when its Marginal Revenue (MR) equals its Marginal Cost (MC): $MR = MC$ .
- The monopolist produces output $Q^*$ where $MR = MC$ .
- The monopolist then sets the price $P^$ for that output $Q^$ by locating the corresponding point on the demand curve.
- No Supply Curve for a Monopoly: Unlike perfectly competitive firms, a monopolist does not have a supply curve because it is a price-setter, not a price-taker, and its output decision is based on both its marginal cost and the shape of the demand curve.
- A monopoly can make profit in the long run because barriers to entry prevent new firms from entering the market to compete away economic profits.
Criticisms of Monopoly:
- Produce too little output: Compared to perfect competition, a monopolist restricts output to keep prices high, leading to an inefficient allocation of resources.
- Potential redistribution of wealth from consumers to owners: Monopolists extract consumer surplus and convert it into producer surplus (profits), which can be seen as an inequitable transfer.
- Produces less output & charges a higher price (compared to perfect competition): This is a direct consequence of market power and profit maximization using MR = MC < P.
- Some consumer surplus under perfect competition is transferred to the monopolist: The higher price and lower quantity under monopoly translate into a portion of consumer surplus becoming monopolist's profit.
- Deadweight loss under monopoly: This is the reduction in total economic surplus (sum of consumer and producer surplus) that results from the monopolist's inefficiently low output and high price. It represents the potential gains from trade that are not realized.
Price Discrimination: A monopolist can practice price discrimination if it can segregate the market into different groups of consumers with different price elasticities of demand.
- Example: Offering discounts to seniors (who may have more elastic demand) compared to other consumers (who may have less elastic demand), thereby charging different prices for the same good.
Diagram Interpretation (Monopoly):
- The demand curve (D) is downward sloping.
- The marginal revenue curve (MR) lies below the demand curve.
- The marginal cost curve (MC) and average cost curve (AC) are shown.
- The monopolist sets output $Q^*$ where $MR = MC$ .
- The price $P^$ is then determined by finding the height of the demand curve at $Q^$ .

11. Pricing in Input Markets

Profit Maximizing Firm's Input Hiring Rule: A firm hires inputs (labor, $L$ , and capital, $K$ ) up to the point where the marginal expense of the input equals the marginal revenue product of that input.
- For labor: $MEL = MRL$
- For capital: $MEK = MRK$
If Firm is Price Taker in Input Markets: In a competitive input market, the marginal expense of an input is simply its market price.
- For labor: $w = MEL = MRL$
- For capital: $v = MEK = MRK$
Marginal Revenue Product (MRP): The extra revenue generated to the firm by hiring an additional unit of an input. It is the product of the marginal product of the input and the marginal revenue from selling the output it produces.
- For labor: $MEL = MRL = MP_L \times MR$
- For capital: $MEK = MRK = MP_K \times MR$
If Firm Sells Output in a Perfectly Competitive Market: In this case, the firm is also a price taker in the output market, so $MR = P$ . The MRP becomes the Marginal Value Product (MVP).
- For labor: $w = MPL \times P = MVPL$ ( $MVP_L$ = marginal value product of labor)
- For capital: $v = MPK \times P = MVPK$ ( $MVP_K$ = marginal value product of capital)
Responses to Changes in Input Prices:
- Single Variable Input (e.g., fixed capital, variable labor):
  - As more labor is hired, the $MVP_L$ falls due to diminishing marginal physical product (i.e., each additional worker contributes less to total output).
  - If the wage rate falls, the firm hires more workers, even if those additional workers add less to total output than previous workers, because their value ( $MVP_L$ ) now exceeds the lower wage ( $w$ ).
- Two Variable Inputs (both labor and capital are variable): A change in an input price triggers two effects:
  1. Substitution Effect: The firm substitutes away from the relatively more expensive input towards the now relatively cheaper input, holding output constant. For example, if the wage ( $w$ ) increases, the firm might use more capital and less labor for the same output level.
    - Size depends on: (i) ease of substitution with other inputs (e.g., how flexible production technology is), and (ii) the length of time available to find substitutes (more time often means more flexibility).
  2. Output Effect: A change in an input price affects the firm's marginal cost of production. For example, a lower input price reduces marginal cost, which encourages the firm to increase its total output. To produce more output, the firm demands more of all inputs.
    - Size depends on: (i) how much marginal cost changes (reflecting the importance of the input to total costs), and (ii) how much output changes in response to a change in the market price (determined by the elasticity of demand for the firm's product).
Responsiveness of Demand to Input Price Changes: For capital and natural resources, supply curves are often upward sloping, meaning higher prices are needed to elicit more supply. For labor, wage increases cause both income and substitution effects, but generally, labor supply tends to increase with wages, though it can become backward-bending at very high wage rates due to a dominant income effect.
Shifts in Demand and Supply for Inputs:
- Changes in marginal productivity of labor: Improvements that increase $MP_L$ will shift the demand curve for labor to the right.
- Technical progress: Can shift the supply curve of inputs (e.g., making capital cheaper or more abundant) or change the demand for inputs (e.g., by making some inputs obsolete or increasing the productivity of others).
Monopsony: A market structure where there is only one buyer (or a single dominant buyer) for a particular input.
- The monopsonist faces an upward-sloping supply curve for the input, meaning it must pay a higher price to hire more units.
- The monopsonist's marginal expense of labor ( $ME_L$ ) curve lies above the supply curve for labor.
- The monopsonist hires the input up to the point where its marginal expense equals the marginal value product of that input: $MEL = MVPL$ .
- Because MEL > w, the monopsonist pays the input less than its marginal value product (w < MVPL).
- This leads to the monopsonist using too little of the input compared to a perfectly competitive input market.
- Examples: A single large employer in a small town, a firm that hires a highly specialized type of input with few alternative buyers, or a cartel of firms that collude in their hiring decisions to act as a single buyer.