Microeconomics Study Guide: Public Goods, Production & Cost, Perfect Competition, and Monopoly

Public Choices, Public Goods, and Common Resources

Types of Goods and Their Characteristics

Goods can be classified based on two key characteristics: rivalry and excludability. Understanding these properties helps explain market outcomes and failures.

• Rivalry: A good is rival if one person's consumption reduces the amount available for others.

• Excludability: A good is excludable if it is possible to prevent people who have not paid from accessing it.

Type of Good	Rival?	Excludable?
Private Goods	Yes	Yes
Club Goods	No	Yes
Common Resources	Yes	No
Public Goods	No	No

• Private Goods: Examples include food, clothing, and cars.

• Club Goods: Examples include subscription services and private parks.

• Common Resources: Examples include fisheries, forests, and public roads.

• Public Goods: Examples include national defense, clean air, and public fireworks displays.

Market Failure and Public Goods

Public goods often lead to market failure because exclusion is difficult and the free rider problem causes private markets to underprovide them.

• Efficient Provision: Occurs where marginal social benefit equals marginal social cost.

• Graphical Logic: For public goods, individual demand (marginal benefit) curves are added vertically to find the total marginal benefit.

Common Resources and the Tragedy of the Commons

Common resources tend to be overused because individuals do not fully account for the external cost imposed on others. This leads to the Tragedy of the Commons: overuse or depletion of a resource due to rivalry and non-excludability.

• Example: Overfishing in a lake where access cannot be restricted.

Production and Cost

Types of Costs

Firms face both explicit and implicit costs in production. Understanding these is essential for analyzing profit and decision-making.

• Explicit Costs: Out-of-pocket payments for resources (e.g., wages, rent).

• Implicit Costs: Opportunity costs of using resources owned by the firm (e.g., owner's time, capital).

• Accounting Cost: Equals explicit cost.

• Economic Cost: Equals explicit cost plus implicit cost.

Profit Calculations

• Accounting Profit: $\text{Accounting Profit} = \text{Total Revenue} - \text{Accounting Cost}$

• Economic Profit: $\text{Economic Profit} = \text{Total Revenue} - \text{Economic Cost}$

Short Run vs. Long Run

• Short Run: At least one input is fixed.

• Long Run: All inputs are variable.

Product Measures

• Total Product (TP): Total output produced.

• Marginal Product (MP): Additional output from one more unit of the variable input.

• Average Product (AP): $\text{AP} = \frac{\text{TP}}{\text{Quantity of Variable Input}}$

• Diminishing Marginal Product: As more units of a variable input are added to fixed inputs, marginal product eventually falls.

• MP intersects AP at the maximum point of AP.

Cost Measures

• Total Cost (TC): $\text{TC} = \text{TFC} + \text{TVC}$

• Average Fixed Cost (AFC): $\text{AFC} = \frac{\text{TFC}}{Q}$

• Average Variable Cost (AVC): $\text{AVC} = \frac{\text{TVC}}{Q}$

• Average Total Cost (ATC): $\text{ATC} = \frac{\text{TC}}{Q} = \text{AFC} + \text{AVC}$

• Marginal Cost (MC): The increase in total cost from producing one more unit of output.

• MC intersects AVC and ATC at their minimum points.

Long-Run Average Cost

• Economies of Scale: Lower average cost at higher output levels.

• Diseconomies of Scale: Higher average cost at very high output levels.

Perfect Competition

Market Structure Characteristics

Perfect competition is a market structure with many firms, homogeneous products, free entry and exit, and perfect information.

• Firms are price takers: The market determines price; individual firms cannot affect it.

Revenue Relationships

• For a perfectly competitive firm: $\text{Demand} = \text{Average Revenue} = \text{Marginal Revenue} = \text{Price}$

Profit Maximization

• The firm chooses output where $\text{MR} = \text{MC}$.

• Since $\text{P} = \text{MR}$ in perfect competition, the profit-maximizing rule is $\text{P} = \text{MC}$ at the chosen output.

• Economic Profit: $\text{Economic Profit} = (\text{P} - \text{ATC}) \times Q$

Short Run Outcomes

• Firms may earn profits, zero economic profit, or losses.

• Break-even Point: $\text{P} = \text{ATC}$, so economic profit is zero.

• Shutdown Condition: In the short run, the firm produces if $\text{P} \geq \text{AVC}$ and shuts down if $\text{P} < \text{AVC}$.

• If $\text{AVC} < \text{P} < \text{ATC}$, the firm operates at a loss in the short run because it covers variable cost and part of fixed cost.

Long Run Outcomes

• Free entry and exit drive economic profit to zero; surviving firms earn zero economic profit.

Monopoly

Market Structure Characteristics

A monopoly exists when a single firm produces a good or service with no close substitutes and significant barriers to entry.

• Monopolist faces a downward-sloping demand curve: Demand equals average revenue; marginal revenue lies below demand.

• For a linear demand curve, MR has the same price intercept as demand and is steeper.

Profit Maximization

• A monopolist chooses output where $\text{MR} = \text{MC}$ and charges the price consumers are willing to pay on the demand curve at that quantity.

• Compared with perfect competition, monopoly produces a lower quantity and charges a higher price.

Price Discrimination

• Charging different prices to different consumers for the same good when price differences are not due to production cost.

• Can increase a monopolist’s profit if the firm can separate markets and limit resale.

Natural Monopoly and Regulation

• Natural Monopoly: One firm can supply the entire market at lower cost than multiple firms due to persistent economies of scale.

• Regulated Marginal Cost Pricing: Regulator sets $\text{P} = \text{MC}$ (allocatively efficient), but if $\text{MC} < \text{ATC}$, the firm may incur losses and require a subsidy.

• Average Cost Pricing: Regulator sets $\text{P} = \text{ATC}$; firm covers all costs and earns zero economic profit, but price is above MC and output is below the allocatively efficient level.

• Two-Part Tariff: Consumers pay a fixed fee plus a per-unit price; helps a natural monopoly cover fixed costs while keeping per-unit price closer to MC.

Profit Calculation and Graphical Representation

• Economic Profit: $\text{Economic Profit} = (\text{P}^* - \text{ATC}^*) \times Q^*$

• On a monopoly graph, profit is the rectangle with height $(\text{P}^* - \text{ATC}^*)$ and width $Q^*$.

Short Run and Long Run Outcomes

• A monopoly can make profits or losses in the short run.

• Shutdown Condition: In the short run, a monopolist continues operating if $\text{P} \geq \text{AVC}$ and shuts down if $\text{P} < \text{AVC}$.

• If losses continue in the long run, the monopolist cannot remain in business indefinitely.

Efficiency and Deadweight Loss

• Because monopoly price exceeds marginal cost at the chosen output, monopoly creates deadweight loss relative to the competitive outcome.

• Example: A monopolist restricts output to raise price, resulting in lost consumer and producer surplus.