AP Microeconomics Unit 5 ReviewFactor Markets

AP Micro Unit 5 flips the supply and demand model around. Instead of firms selling products to consumers, firms are now the buyers, purchasing labor, capital, and land from households, and the price of each resource (wages, interest, rent) is set by supply and demand in those factor markets. The single biggest idea is the hiring rule. A profit-maximizing firm hires workers up to the point where the marginal revenue product of labor equals the marginal factor cost of labor (MRP = MFC). Unit 5 makes up 10-13% of the AP exam.

What this unit covers

Derived demand and the basics of factor markets

• In factor markets, the roles from product markets reverse. Households supply resources (their labor, their savings, their land), and firms demand them. Wages, interest, and rent are just prices in these markets.
• Factor demand is derived demand. A firm doesn't want workers for their own sake. It wants the output workers produce. Demand for pizza chefs comes from demand for pizza. If pizza demand falls, so does demand for pizza chefs, even if the chefs are exactly as skilled as before.
• The labor demand curve slopes downward. As the wage falls, firms want to hire more workers. The labor supply curve slopes upward. As the wage rises, more people are willing to work in that market.
• The market wage and quantity of labor come from where labor supply meets labor demand, just like price and quantity in Unit 2. Same logic, new axis labels (wage on the vertical, quantity of labor on the horizontal).

MRP, MFC, and the hiring rule

• Marginal revenue product (MRP) is the extra revenue one more worker brings in. Compute it as marginal product times the price of the output (in a competitive product market), or more generally as the change in total revenue from hiring one more unit. So MRP = MP x P, or MRP = ΔTR / ΔL.
• Marginal factor cost (MFC), also called marginal resource cost, is the extra cost of hiring one more unit of the input. In a competitive labor market, MFC is just the wage.
• The hiring rule is the same marginal logic that runs the whole course. Hire as long as the worker adds more revenue than cost (MRP > MFC), stop when MRP = MFC. This is marginal benefit equals marginal cost, applied to inputs instead of output.
• MRP falls as you hire more workers because of diminishing marginal returns from Unit 3. The fourth barista adds less output than the third when there's only one espresso machine. That falling MRP curve IS the firm's labor demand curve.
• Expect to calculate MRP and MFC from a table. You'll be given workers hired, total output, and the product price, and asked how many workers the firm hires at a given wage.

Shifters of labor demand and labor supply

• Labor demand shifts when the output price changes (higher product price raises MRP at every quantity, shifting demand right) or when worker productivity changes (better training or technology raises MP, which raises MRP).
• Labor supply shifts with things like immigration, education and training, working conditions, the age distribution of the population, availability of alternative jobs, preferences for leisure, and cultural expectations.
• Keep the movement-versus-shift distinction from Unit 2. A wage change causes movement along the curves. A change in a determinant shifts a curve. A minimum wage doesn't shift labor supply, it puts a price floor in the labor market.

Competitive labor markets vs. monopsony

• In a perfectly competitive labor market, many firms hire identical workers, and each firm is a wage taker. The firm faces a perfectly elastic (horizontal) labor supply curve at the market wage, so wage = MFC. The firm hires where MRP = wage.
• Important subtlety here. A firm can be a perfect competitor in the labor market even while being a monopoly in its product market. The two market structures are independent.
• A monopsony is a single buyer of labor, like the only hospital in a small town hiring nurses. To hire one more worker, the monopsonist has to raise the wage, and it raises the wage for everyone it already employs. That makes MFC greater than the wage, so the MFC curve sits above the labor supply curve.
• The monopsonist hires where MRP = MFC, but then pays the wage off the labor supply curve at that quantity. Result: fewer workers hired and a lower wage than a competitive market would deliver. Workers are paid less than their MRP.

Unit 5, Factor Markets at a glance

Why Unit 5, Factor Markets matters in AP Micro

This unit proves the course's central claim, that rational decision-makers compare marginal benefit and marginal cost, works on the input side too. Everything you learned about firms choosing output now repeats for firms choosing inputs, and the parallels are exactly what the exam tests.

• The MRP = MFC hiring rule is the input-market twin of the MR = MC output rule. Same logic, different decision.
• Monopsony shows that market power matters on the buyer side too. Just as a monopoly restricts output and raises price, a monopsony restricts hiring and lowers the wage.
• Factor markets explain real outcomes you care about, like why wages differ across jobs and why a single dominant employer in a town can pay workers less than they're worth.

How this unit connects across the course

• The labor market graph is the supply and demand model from Supply and Demand (Unit 2) with new labels. Shifters, equilibrium, and price floors (minimum wage) all transfer directly.
• Diminishing marginal returns from Production, Cost, and Perfect Competition (Unit 3) is why MRP falls as hiring rises, and the MRP = MFC rule mirrors the MR = MC profit-maximization rule for output.
• Monopsony is the hiring-side version of monopoly from Imperfect Competition (Unit 4). Where a monopolist's MR sits below demand, a monopsonist's MFC sits above labor supply. Knowing one graph helps you draw the other.
• A minimum wage in a competitive labor market creates unemployment, but in a monopsony it can actually raise both wage and employment. That kind of government intervention analysis is the heart of Market Failure and the Role of Government (Unit 6).

Key models and graphs to know

• Competitive labor market side-by-side graph: the market panel (upward labor supply, downward labor demand) sets the equilibrium wage; the firm panel shows a horizontal MFC at that wage crossing the firm's downward-sloping MRP curve at the profit-maximizing quantity of labor.
• MRP and MFC table calculations: given workers, total product, and output price, compute MP, then MRP = MP x P, and hire every worker whose MRP is at least the wage.
• Monopsony graph: upward-sloping labor supply, MFC curve above it, downward-sloping MRP. Quantity comes from MRP = MFC; the wage comes from dropping down to the supply curve at that quantity.
• Labor demand and supply shift graphs: show how a productivity boost, an output price change, or immigration moves the equilibrium wage and employment.
• Minimum wage in a labor market: a binding price floor above equilibrium creates a surplus of labor (unemployment) in a competitive market.

Unit 5, Factor Markets on the AP exam

Factor markets are 10-13% of the exam, which usually means a cluster of multiple-choice questions plus a strong chance of appearing in a short free-response question. Here's what you'll actually do with this content:

• Calculate MRP and MFC from a table and decide how many workers a firm hires at a given wage. This is the most common factor-market task, and the answer is always "hire until MRP would fall below MFC."
• Draw and label labor market graphs, including the side-by-side competitive market and firm graphs and the monopsony graph with MFC above supply. Accurate labels (wage axis, MRP, MFC, S of labor) earn points.
• Predict how a shift in labor demand or supply changes the equilibrium wage and quantity of labor, and identify which determinant caused the shift.
• Compare outcomes across market structures, such as showing that a monopsony pays a lower wage and hires fewer workers than a competitive market, or analyzing what a minimum wage does in each setting.
• Watch for combination questions that mix product-market and factor-market structure, like a monopolist in the output market hiring in a competitive labor market. Keep the two decisions separate.

Essential questions

• Why does a firm's demand for workers depend on consumers' demand for the firm's product?
• How does a profit-maximizing firm decide exactly how many workers to hire?
• What happens to wages and employment when one firm is the only buyer of labor in a market?
• How do changes in productivity, output prices, and population shifts ripple through labor markets to change wages?

Key terms to know

• Derived demand: demand for an input that comes from demand for the product the input produces.
• Marginal revenue product (MRP): the additional revenue from employing one more unit of an input, equal to MP x P in a competitive product market.
• Marginal factor cost (MFC): the additional cost of employing one more unit of an input; also called marginal resource cost.
• Marginal product (MP): the additional output from one more unit of an input, holding other inputs fixed.
• Wage taker: a firm in a perfectly competitive labor market that hires any amount of labor at the market wage.
• Monopsony: a market with a single buyer, who must raise the wage for all workers to hire one more, making MFC exceed the wage.
• Factors of production: labor, capital, and land, the inputs firms buy in factor markets.
• Factor prices: the payments to inputs, namely wages for labor, interest for capital, and rent for land.
• Labor supply determinants: non-wage influences like immigration, education, working conditions, and preferences for leisure that shift the labor supply curve.
• Labor demand determinants: changes in output price or worker productivity that shift the labor demand (MRP) curve.
• Least-cost rule: hiring inputs so the marginal product per dollar is equal across inputs, MP_L / P_L = MP_K / P_K.

Common mix-ups

• MRP = MFC is the hiring rule for inputs; MR = MC is the output rule. They use the same logic but answer different questions ("how many workers?" vs. "how much output?"). Don't swap them on an FRQ.
• A wage change does NOT shift labor demand or labor supply. It moves you along the curves. Only the determinants (productivity, output price, immigration, preferences) shift them.
• In a monopsony, the firm hires where MRP = MFC but does not pay that amount. The wage comes from the labor supply curve at the chosen quantity, which is lower. Reading the wage off the wrong curve is the most common monopsony graph error.
• A firm's structure in the product market and the labor market are independent. A monopoly seller can still be a wage taker, and a competitive seller could in theory be a monopsonist.