Oligopoly can be defined in terms of market structure or market conduct (behaviour)
Economists define oligopoly in two ways. One looks at how the market is built — a few large firms dominating. The other looks at how those firms actually behave toward each other.
Real World
The UK banking sector is an oligopoly by structure (Lloyds, Barclays, HSBC, NatWest dominate), but also by conduct — banks have historically moved interest rates in parallel, suggesting coordinated behaviour without explicit agreement.
Exam Focus
Distinguish clearly between structure (concentration ratios) and conduct (interdependent behaviour) — conflating them is a common exam error.
Price Elasticity of Demand
PED = % change in quantity demanded ÷ % change in price
How well did you know this?