Market structure Study Guide

📖 Core Concepts Market Structure – The way firms are grouped by the type of goods they sell (homogeneous vs. heterogeneous) and by market features such as number of sellers, entry barriers, and pricing rules. Participants – Suppliers (firms) and demanders (consumers) are equally essential; their interaction drives price formation toward an equilibrium price‑quantity pair. Core Elements – Number/size of sellers, entry‑exit barriers, product nature, pricing mechanism, and selling costs together define a market’s structure. Competitive Spectrum – From most to least competitive: Perfect Competition → Monopolistic Competition → Oligopoly → Monopoly. Price‑Maker vs. Price‑Taker – In perfect competition firms take the market price; in monopoly the single firm makes the price. --- 📌 Must Remember Perfect Competition – Many buyers/sellers, free entry‑exit, homogeneous product, firms are price takers; long‑run price = lowest point on ATC. Monopolistic Competition – Many sellers, differentiated but close‑substitutes, some price power, low‑moderate entry barriers. Oligopoly – Few dominant firms, high entry barriers, interdependent decisions, often price‑rigid; analyzed with game theory (Nash equilibrium). Duopoly Models Cournot: Firms choose quantities → total output sets market price. Bertrand: Firms choose prices → lower‑price firm captures the market (if products homogeneous). Monopoly – Single seller, no close substitutes, price maker, high barriers; natural monopoly when economies of scale make one firm cheapest. Monopsony – Single buyer (e.g., dominant employer) → can push wages/prices down. Concentration Measures $CRN = \displaystyle\sum{i=1}^{N} si$ (share of top N firms). $HHI = \displaystyle\sum{i=1}^{n} si^{2}$ (sum of squared market shares, 0–10 000 when shares are percentages). Price Discrimination – Three levels (first‑, second‑, third‑degree); first‑degree can eliminate consumer surplus. --- 🔄 Key Processes Short‑Run Decision in Perfect Competition Compare price (P) to marginal cost (MC). If P > MC → increase output; if P < MC → cut output. Long‑Run Adjustment (Perfect Competition) Positive profits → entry → supply ↑ → price ↓ → profits → 0. Losses → exit → supply ↓ → price ↑ → losses → 0. Cournot Quantity Competition Each firm selects $qi$ assuming rival’s $qj$ fixed. Market price: $P = a - b(Q)$ where $Q = \sum qi$. Solve first‑order condition: $\frac{\partial \pii}{\partial qi}=0$ for each firm → Nash equilibrium quantities. Bertrand Price Competition (Homogeneous Goods) Firms set $pi$ simultaneously. The firm with the lower price captures whole market (price = marginal cost in equilibrium). Assessing Market Power Compute $CRN$ and $HHI$. HHI > 2,500 → highly concentrated (possible antitrust concern). --- 🔍 Key Comparisons Perfect Competition vs. Monopoly Many vs. single sellers. Price taker vs. price maker. Zero economic profit long‑run vs. positive economic profit possible. Cournot vs. Bertrand Cournot: firms choose quantities → higher prices. Bertrand: firms choose prices → price driven to marginal cost (if products identical). Oligopoly vs. Monopolistic Competition Oligopoly: few large firms, strategic interdependence. Monopolistic competition: many small firms, limited strategic effects. Natural Monopoly vs. Regular Monopoly Natural: cost structure (economies of scale) justifies single firm. Regular: monopoly power from barriers, not necessarily cost advantage. --- ⚠️ Common Misunderstandings “All oligopolies collude.” → Many maintain price rigidity without explicit collusion; competition can still be fierce. “High HHI always means monopoly.” → A high HHI indicates concentration, but a few firms may still compete (oligopoly). “Price discrimination always benefits consumers.” → First‑degree discrimination can wipe out consumer surplus; other forms may shift surplus to the firm. “Entry barriers = no new firms ever.” → Barriers are relative; high‑tech or regulatory changes can lower them over time. --- 🧠 Mental Models / Intuition “Market as a balance beam.” – Suppliers push price up (costs), demanders pull price down (willingness to pay); equilibrium is where the beam balances. “Game‑theory chessboard.” – In oligopoly each firm’s move (price or quantity) anticipates the rival’s response; think of each decision as a chess move toward a Nash equilibrium. “Network effect snowball.” – More users on one side of a platform attract even more users on the other side, creating a self‑reinforcing growth loop. --- 🚩 Exceptions & Edge Cases Natural Monopoly – Single firm is efficient due to declining average costs; regulation (price caps) may be needed. First‑Degree Price Discrimination – Requires perfect information on each buyer’s willingness to pay; rarely fully achievable. Platform Markets – May exhibit two‑sided network effects; pricing may be asymmetric (one side subsidized). Oligopsony – Few buyers can depress input prices, opposite of oligopoly’s buyer power. --- 📍 When to Use Which Choose Cournot when firms compete mainly on output (e.g., capacity‑constrained industries). Choose Bertrand when firms set prices for identical products (e.g., commodity markets). Use HHI for a detailed competition assessment (captures distribution of all firms). Use CRN for a quick snapshot of market share concentration among the largest players. Apply game theory for any oligopolistic scenario where strategic interaction matters (price wars, capacity decisions). --- 👀 Patterns to Recognize Few large market shares + high HHI → oligopoly or monopoly. Differentiated products + many sellers → monopolistic competition. Zero economic profit in the long run + price = MC → perfect competition. Price rigidity despite cost changes → likely oligopoly. Two distinct user groups with cross‑group subsidies → platform market with network effects. --- 🗂️ Exam Traps “A high concentration ratio automatically means antitrust violation.” – Regulators look at HHI, market dynamics, and entry barriers, not just CR. “Bertrand competition always yields zero profit.” – Only true when products are perfect substitutes and there are no capacity constraints. “Monopolistic competition has no profit in the long run.” – Firms earn normal profit (zero economic profit) but can still enjoy positive accounting profit due to product differentiation. “Natural monopoly always requires government ownership.” – Often regulated private ownership is sufficient; ownership choice depends on policy goals. ---