Market Structures and Input Demand in Microeconomics: Study Notes

Input Demand: The Labor and Land Markets

Derived Demand and Marginal Revenue Product of Labor (MRPL)

In input markets, the demand for labor and land is derived from the demand for the final goods and services produced. Firms hire inputs to maximize profit, and the value of an additional unit of labor is measured by its marginal revenue product.

• Derived Demand: The demand for an input (e.g., labor) that depends on the demand for the output it helps produce.

• Marginal Revenue Product of Labor (MRPL): The additional revenue generated from employing one more unit of labor. It is calculated as: $MRPL = MPL \times P_X$ where MPL is the marginal product of labor and PX is the price of the output.

• Diminishing MRPL: As more labor is hired, the marginal product of labor typically decreases, leading to a diminishing MRPL.

Profit-Maximizing Condition (Short Run): Firms hire labor up to the point where MRPL equals the wage rate (W): $MRPL = W$

• When multiple variable inputs are used (e.g., labor and capital), a change in the wage rate affects the demand for both inputs.

• Profit-Maximizing Condition (Multiple Inputs): The last dollar spent on each input should yield the same marginal product: $\frac{MP_L}{P_L} = \frac{MP_K}{P_K}$ If $\frac{MP_L}{P_L} > \frac{MP_K}{P_K}$, the firm should use more labor and less capital until equality is restored.

Market Structures

Perfect Competition

Perfect competition is a market structure characterized by many firms selling identical products, with no single firm able to influence the market price.

• Firms are price takers with no market power.

• The demand curve facing an individual firm is perfectly elastic (horizontal at the market price).

• Profit-maximizing output is where $P = MR = MC$.

• Free entry and exit in the long run ensure zero economic profit and efficient production at the lowest average total cost (ATC).

Monopoly

A monopoly exists when a single firm is the sole producer of a product with no close substitutes, often due to barriers to entry.

• Monopolists are price makers with significant market power.

• Profit-maximizing output is where marginal revenue equals marginal cost ($MR = MC$), but price is set above marginal cost ($P > MC$).

• Monopolists can earn positive economic profits in the long run due to barriers to entry.

• Monopoly leads to a higher price and lower quantity compared to perfect competition, resulting in a deadweight loss (DWL) and reduced total surplus.

Price Discrimination

• Single Price Monopoly: The monopolist charges the same price to all buyers, resulting in consumer surplus, monopoly profit, and deadweight loss.

• Perfect Price Discrimination: The monopolist charges each buyer their maximum willingness to pay, capturing all consumer surplus as profit and eliminating deadweight loss.

Oligopoly

An oligopoly is a market structure with a few firms selling similar or identical products. Firms are interdependent and often engage in strategic behavior.

• High concentration ratio; firms may collude to act like a monopoly, but have incentives to cheat.

• Game theory is used to analyze strategic interactions, including dominant strategies and Nash equilibrium.

• As the number of firms increases, the market outcome approaches that of perfect competition ($P \rightarrow MC$).

• Collusion can lead to monopoly-like outcomes, but self-interest often prevents stable collusion.

• Typical outcome: $Q_M < Q_O < Q_C$ and $P_C < P_O < P_M$ (where subscripts M = monopoly, O = oligopoly, C = competition).

Monopolistic Competition

Monopolistic competition features many firms selling differentiated products. Firms have some market power due to product differentiation.

• Short run: Firms behave like monopolists, setting price above marginal cost.

• Long run: Free entry and exit drive economic profit to zero, similar to perfect competition.

• Firms do not produce at minimum ATC, resulting in excess capacity and inefficiency.

• There is a markup of price over marginal cost ($P > MC$).

Comparison of Market Structures

The following table summarizes the key characteristics of perfect competition, monopolistic competition, and monopoly:

	Perfect competition	Monopolistic competition	Monopoly
Number of sellers	many	many	One
Free entry/exit	yes	yes	no
LR econ. Profits	zero	zero	positive
The products firms sell	identical	differentiated	One product
Firm has market power?	None, price-taker	yes	yes
D curve facing firm	horizontal	downward-sloping	downward-sloping
Close substitutes	None	many	None