Microeconomics: Markets, Firms, and Policy

Scarcity, Choice, and Marginal Reasoning

Microeconomics studies how individuals, firms, and governments make choices when resources are scarce. Scarcity means that resources are limited relative to wants, so every choice involves a trade-off.

The central decision rule is marginal analysis. Compare the additional benefit and additional cost of an action:

The optimal quantity usually occurs where $MB=MC$. A rational decision does not necessarily maximize total benefit by itself; it compares the next increment of benefit with the next increment of cost. Incentives such as prices, taxes, rewards, and penalties change the costs and benefits that guide behavior.

Opportunity cost is the value of the next-best alternative forgone. If a person can work for $\$18$ during an additional hour or study instead, the opportunity cost of studying is $\$18$. If the expected benefit of studying is $\$25$, its net benefit is $\$7$, assuming no other relevant changes.

Positive statements describe what is or can be observed. Normative statements express judgments about what should occur. Keeping these categories separate helps distinguish economic analysis from policy preferences.

Takeaway: Identify the decision-maker, objective, marginal comparison, incentive, and opportunity cost before solving an unfamiliar problem.

Production Possibilities and Efficiency

A production possibilities curve shows the maximum combinations of two goods that can be produced with available resources and technology. A point on the curve is productively efficient. A point inside the curve is attainable but inefficient, while a point outside the curve is unattainable under current conditions.

The slope of the curve represents the opportunity cost of producing more of one good in terms of the other. A bowed-out curve indicates increasing opportunity cost because resources are not equally suited to producing both goods. Improved technology or additional resources can shift the curve outward and represent economic growth.

Efficiency has several distinct meanings:

• Productive efficiency means producing at the lowest possible average total cost.

• Allocative efficiency means producing where marginal benefit equals marginal cost.

• Economic efficiency means maximizing total surplus.

• Equity concerns the fairness of an outcome or distribution and is distinct from efficiency.

A market can be efficient without producing an outcome that everyone considers fair. Evaluating policy therefore requires attention to both efficiency and distribution.

Consumer Choice and Demand

Consumers face a budget constraint that limits the combinations of goods they can afford at given prices and income. They attempt to maximize utility, or satisfaction from consumption.

Marginal utility is the additional satisfaction from one more unit. With diminishing marginal utility, each additional unit provides less additional satisfaction than the preceding unit. Spending is allocated efficiently when marginal utility per dollar is equal across goods:

If one good provides a higher marginal utility per dollar, the consumer can increase total utility by shifting spending toward that good.

A demand curve shows the quantity consumers are willing and able to buy at different prices, holding other influences constant. A change in the good's own price causes movement along the demand curve. A change in another determinant shifts the entire curve.

Important demand shifters include income, tastes, expectations, the number of buyers, and prices of related goods. A rise in income increases demand for a normal good but decreases demand for an inferior good. A rise in the price of a substitute increases demand for the good being considered, while a rise in the price of a complement decreases it.

Consumer surplus is the difference between a buyer's willingness to pay and the price actually paid. On a standard graph, it is the area below the demand curve and above the market price, up to the quantity purchased.

Takeaway: First ask whether the good's own price changed. If it did, move along the curve; otherwise identify the determinant that shifts demand.

Production, Costs, and Profit

A firm combines land, labor, capital, and entrepreneurship to produce output. In the short run, at least one input is fixed. In the long run, all inputs are variable.

Total product is total output. Marginal product is the additional output from one more unit of an input, and average product is output per unit of input. For labor:

The law of diminishing marginal returns occurs when additional units of a variable input eventually add smaller increments to output, usually because at least one input is fixed in the short run.

The main cost relationships are:

Fixed cost does not change with output in the short run, whereas variable cost changes as output changes. Average fixed cost declines as output rises because fixed cost is spread over more units. Marginal cost often falls initially and then rises as diminishing marginal returns appear. The marginal cost curve intersects the average variable cost and average total cost curves at their minimum points.

Economic profit equals total revenue minus total economic cost. Economic cost includes explicit payments, such as wages and rent, and implicit opportunity costs of owner-supplied resources.

A firm increases output while $MR>MC$, decreases output when $MR<MC$, and reaches its profit-maximizing quantity where $MR=MC$.

Supply, Demand, and Market Welfare

Market equilibrium occurs where quantity demanded equals quantity supplied. A shortage occurs when quantity demanded exceeds quantity supplied, usually because the price is below equilibrium. A surplus occurs when quantity supplied exceeds quantity demanded, usually because the price is above equilibrium.

Supply generally slopes upward because higher prices create incentives for firms to produce more. Supply increases when input prices fall, technology improves, taxes decrease, subsidies increase, the number of sellers rises, or production conditions become more favorable. Supply decreases under the reverse conditions.

Use a four-step shift method:

1. Draw the original demand and supply curves.

2. Identify whether the event affects demand, supply, or both.

3. Determine the direction of the shift.

4. Compare the new equilibrium price and quantity with the original values.

For example, if demand and supply are $Q_d=100-2P$ and $Q_s=20+2P$, equilibrium satisfies:

Total surplus equals consumer surplus plus producer surplus. Producer surplus is the difference between the price received and the minimum price a seller would accept. In a properly functioning competitive market without external costs or benefits, equilibrium can maximize total surplus. When mutually beneficial trades fail to occur, the result is deadweight loss.

Takeaway: For every shift, state the direction of the curve movement and the resulting changes in both equilibrium price and quantity.

Elasticity and Tax Incidence

Elasticity measures the responsiveness of one variable to a change in another. Price elasticity of demand is:

Because price and quantity demanded usually move in opposite directions, $PED$ is often negative; classification generally uses its absolute value. Demand is elastic when the absolute value exceeds $1$, unit elastic when it equals $1$, and inelastic when it is less than $1$. For a change between two points, use the midpoint formula:

Demand tends to be more elastic when close substitutes exist, the good is narrowly defined, the good is a luxury, consumers have more time to adjust, or the good takes a large share of income.

Total revenue is:

When demand is elastic, a price increase reduces total revenue. When demand is inelastic, a price increase increases total revenue. With unit-elastic demand, total revenue is approximately unchanged by a price change.

Other useful measures include price elasticity of supply, income elasticity of demand, and cross-price elasticity of demand. A positive income elasticity indicates a normal good, while a negative value indicates an inferior good. A positive cross-price elasticity indicates substitutes, while a negative value indicates complements.

Supply is generally more elastic in the long run because firms have more time to adjust inputs and capacity. The relatively more inelastic side of a market generally bears the larger share of a per-unit tax.

Government Intervention in Markets

Government policies can change prices, quantities, distribution, and efficiency. A binding price ceiling is set below equilibrium and creates a shortage. Likely consequences include queues, rationing, lower quality, and black markets. A ceiling above equilibrium is nonbinding.

A binding price floor is set above equilibrium and creates a surplus. A minimum wage is a price floor in the labor market and can create a surplus of labor, measured as unemployment. A floor below equilibrium is nonbinding.

A per-unit tax creates a wedge between the price paid by buyers and the price received by sellers:

Taxes generally increase the buyer price, reduce the seller's net price, lower the quantity exchanged, generate government revenue, and create deadweight loss. Tax revenue is:

A subsidy lowers the effective cost of production or consumption and usually increases the quantity exchanged. It may also require government spending and encourage overproduction relative to the efficient level.

Policy should be evaluated using both efficiency and distribution. A tax may reduce a harmful externality, but it also changes consumer and producer surplus. A price control may help some participants while creating shortages or surpluses for others.

Takeaway: Check whether an intervention is binding, identify the affected prices and quantity, and evaluate surplus as well as the policy's intended goal.

Market Structures and Firm Strategy

Market structures differ in the number of firms, product characteristics, barriers to entry, pricing power, and long-run outcomes.

In perfect competition, many firms sell identical products, entry is easy, and each firm is a price taker. The firm faces:

It chooses output where $P=MC$. In the short run, it operates if price is at least average variable cost. It shuts down when $P<AVC$ at the relevant output. In the long run, it exits if price remains below average total cost and breaks even when $P=ATC$.

A monopoly has one seller, high barriers to entry, and a downward-sloping demand curve. Because the monopolist must lower price to sell more output, marginal revenue lies below demand. The firm chooses quantity where $MR=MC$, then finds the highest price consumers will pay for that quantity on the demand curve. Compared with competition, monopoly usually produces less, charges more, and creates deadweight loss. A natural monopoly exists when economies of scale make one large producer less costly than several smaller producers.

Monopolistic competition has many firms selling differentiated products. Firms compete through price, quality, location, service, and advertising. Entry and exit tend to eliminate long-run economic profit, but firms may have excess capacity and price above marginal cost.

An oligopoly has a few strategically interdependent firms. A dominant strategy is best regardless of the rival's action. A Nash equilibrium is a set of strategies in which no player benefits by changing strategy alone. Collusion coordinates firms to restrict output or raise price, but a cartel may be unstable because each member has an incentive to cheat.

Takeaway: Identify the structure first, then apply its pricing rule, entry condition, and efficiency implications.

Factor Markets and Labor Decisions

Factor markets allocate labor, land, capital, and entrepreneurship. Demand for an input is derived demand because firms want the input for what it helps produce.

The marginal revenue product of an input is:

In a perfectly competitive product market:

A profit-maximizing firm hires an input up to the point where:

where $MFC$ is marginal factor cost. In a competitive labor market, the wage is the marginal factor cost of labor. If $MRP>\text{wage}$, hiring another worker increases profit; if $MRP<\text{wage}$, employment should be reduced.

Labor demand increases when product demand or product price rises, worker productivity increases, the price of a substitute input rises, or the price of a complementary input falls. Labor supply increases when the opportunity cost of working falls, working conditions improve, immigration increases, or more people enter the labor force.

A binding minimum wage can create a surplus of labor. Economic rent is payment to a factor above the minimum required to keep it in its current use. Scarce land, highly specialized workers, and unusually talented performers may receive substantial economic rent because their supply is limited.

Takeaway: To analyze a factor-market problem, calculate the input's marginal revenue product and compare it with the marginal factor cost.

Market Failure and Public Policy

Market failure occurs when an unregulated market does not allocate resources efficiently. Common causes include externalities, public goods, common resources, and asymmetric information.

An externality affects a third party outside the transaction. A negative production externality, such as pollution, makes marginal social cost exceed marginal private cost:

Because producers do not bear the full cost, the market quantity is usually greater than the socially efficient quantity. A corrective tax, regulation, tradable permits, or clearly defined property rights can reduce the external cost.

A positive externality creates a benefit for third parties. Vaccination can benefit people beyond the person receiving it. Marginal social benefit exceeds marginal private benefit:

The market quantity is usually below the socially efficient quantity, so a subsidy or public provision can encourage additional consumption or production.

A pure public good is nonrival and nonexcludable. The free-rider problem may cause private markets to underprovide it. A common resource is rival but difficult to exclude others from using, so open access can create the tragedy of the commons.

Asymmetric information exists when one party has more relevant information than another. Adverse selection involves hidden information before a transaction, while moral hazard involves hidden action after a transaction. Warranties, disclosure, licensing, screening, monitoring, and insurance contracts can reduce these problems.

Government intervention can improve efficiency but can also create government failure through poor information, administrative costs, unintended incentives, regulatory capture, or political pressure.

A Unified Problem-Solving Framework

A reliable solution method connects the model, equation, graph, and economic interpretation.

1. Identify the decision-maker or market: consumer, firm, factor market, government, or whole market.

2. State the objective: consumers maximize utility, firms maximize profit, and policy may pursue efficiency, equity, or another goal.

3. Choose the model: supply and demand, cost curves, market structure, factor demand, externality analysis, or game theory.

4. Write the governing rule, such as $MB=MC$, $MR=MC$, $P=MC$, $MRP=MFC$, or $Q_d=Q_s$.

5. Draw the graph when required, labeling axes, original and new curves, equilibrium points, prices, quantities, and welfare regions.

6. Substitute values carefully and show units, signs, and intermediate steps.

7. Interpret the result: state who gains, who loses, how price and quantity change, and whether efficiency changes.

8. Check the result against the model.

Useful checks include:

• A binding price ceiling creates a shortage.

• A binding price floor creates a surplus.

• A tax reduces the quantity exchanged.

• A negative externality implies $MSC>MPC$.

• A positive externality implies $MSB>MPB$.

• A competitive firm operates in the short run when $P\ge AVC$.

• A monopolist chooses quantity using $MR=MC$, then obtains price from demand.

For calculation practice, equilibrium from $Q_d=120-3P$ and $Q_s=20+2P$ gives $P=20$ and $Q=60$. A competitive firm with $P=14$, $Q=30$, and $TC=330$ earns $\$90$, because total revenue is $\$420$. A worker with $MP=8$ and product price $\$25$ has $MRP=\$200$, so the worker should be hired when the wage is $\$180$.