The Nature and Functions of Product Markets
What this domain tests
Product markets covers demand and supply, elasticity, consumer and producer surplus, tax incidence, short-run and long-run costs, profit maximization, and the four market structures. Expect graph-free numerical questions and cause-effect reasoning about shifts and controls.
Demand, supply, and equilibrium
- Demand determinants include income, tastes, prices of substitutes and complements, expectations, and number of buyers. Supply determinants include input costs, technology, taxes and subsidies, expectations, and number of sellers.
- A change in the good's own price is a movement along the curve; a change in a determinant is a shift.
- A binding price ceiling creates a shortage; a binding price floor creates a surplus. Both reduce quantity traded and create deadweight loss.
Elasticity and tax incidence
- Price elasticity of demand = %Δ quantity ÷ %Δ price. Demand is elastic if the absolute value exceeds 1, inelastic if below 1. The total revenue test: price cuts raise revenue when demand is elastic.
- Determinants: availability of substitutes, necessity versus luxury, budget share, and time horizon.
- Tax incidence: legal assignment does not matter. The burden falls more heavily on the more inelastic side of the market. Deadweight loss grows as demand and supply become more elastic.
Costs, profit, and market structure
- Economic profit subtracts implicit and explicit costs; accounting profit subtracts only explicit costs.
- Marginal cost crosses average total cost at minimum ATC. Profit maximization occurs where MR = MC; a firm shuts down in the short run if price falls below AVC.
- Perfect competition: P = MR; long-run equilibrium at minimum ATC with zero economic profit. Monopoly: MR < P, barriers to entry, deadweight loss. Monopolistic competition: differentiated products, zero long-run profit. Oligopoly: strategic interdependence, game theory, Nash equilibrium.
Worked example
Demand is P = 100 − Q and supply is P = 20 + Q. Equilibrium sets 100 − Q = 20 + Q, so Q = 40 and P = 60. A $12 per-unit tax on sellers shifts supply to P = 32 + Q. Then 100 − Q = 32 + Q gives Q = 34 and P = 66. Consumers pay 66, up $6; sellers receive 66 − 12 = 54, down $6. The split is equal because the curves have equal absolute slopes. Tax revenue is 12 × 34 = 408, and deadweight loss is ½ × 12 × (40 − 34) = 36.
Traps that cost marks
- Confusing a shift with a movement along a curve.
- Using P = MC for a monopolist instead of MR = MC.
- Ignoring implicit costs when computing economic profit.
- Treating elasticity as slope; steep curves can still be elastic at high prices.
- Assuming the party that legally pays a tax bears its burden.